diff --git a/Jenkinsfile b/Jenkinsfile
index 83104aea18..de62b7ed5a 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -1,5 +1,6 @@
 parallel_nodes(['linux && cura', 'windows && cura']) {
     timeout(time: 2, unit: "HOURS") {
+
         // Prepare building
         stage('Prepare') {
             // Ensure we start with a clean build directory.
diff --git a/cura/Machines/MaterialManager.py b/cura/Machines/MaterialManager.py
index 8b9fb2391c..5d691fcef4 100644
--- a/cura/Machines/MaterialManager.py
+++ b/cura/Machines/MaterialManager.py
@@ -378,9 +378,8 @@ class MaterialManager(QObject):
             # Look at the guid to material dictionary
             root_material_id = None
             for material_group in self._guid_material_groups_map[material_guid]:
-                if material_group.is_read_only:
-                    root_material_id = material_group.root_material_node.metadata["id"]
-                    break
+                root_material_id = material_group.root_material_node.metadata["id"]
+                break
 
             if not root_material_id:
                 Logger.log("i", "Cannot find materials with guid [%s] ", material_guid)
diff --git a/cura/Settings/ContainerManager.py b/cura/Settings/ContainerManager.py
index 657329aad4..216637db21 100644
--- a/cura/Settings/ContainerManager.py
+++ b/cura/Settings/ContainerManager.py
@@ -5,7 +5,7 @@ import os
 import urllib.parse
 import uuid
 from typing import Any
-from typing import Dict, Union
+from typing import Dict, Union, Optional
 
 from PyQt5.QtCore import QObject, QUrl, QVariant
 from PyQt5.QtWidgets import QMessageBox
@@ -46,14 +46,19 @@ class ContainerManager(QObject):
         self._quality_manager = self._application.getQualityManager()
         self._container_name_filters = {}   # type: Dict[str, Dict[str, Any]]
 
-    @pyqtSlot(str, str, result=str)
-    def getContainerMetaDataEntry(self, container_id, entry_name):
+    @pyqtSlot(str, str, str, result=str)
+    def getContainerMetaDataEntry(self, container_id, entry_name, sub_entry: Optional[str] = None):
         metadatas = self._container_registry.findContainersMetadata(id = container_id)
         if not metadatas:
             Logger.log("w", "Could not get metadata of container %s because it was not found.", container_id)
             return ""
 
-        return str(metadatas[0].get(entry_name, ""))
+        sub_data = metadatas[0].get(entry_name, "")
+        result = str(sub_data)
+        if sub_entry:
+            result = str(sub_data.get(sub_entry, ""))
+
+        return result
 
     ##  Set a metadata entry of the specified container.
     #
diff --git a/plugins/3MFReader/ThreeMFReader.py b/plugins/3MFReader/ThreeMFReader.py
index 6bfe920863..0280600834 100755
--- a/plugins/3MFReader/ThreeMFReader.py
+++ b/plugins/3MFReader/ThreeMFReader.py
@@ -169,8 +169,6 @@ class ThreeMFReader(MeshReader):
             archive = zipfile.ZipFile(file_name, "r")
             self._base_name = os.path.basename(file_name)
             parser = Savitar.ThreeMFParser()
-            with open("/tmp/test.xml", "wb") as f:
-                f.write(archive.open("3D/3dmodel.model").read())
             scene_3mf = parser.parse(archive.open("3D/3dmodel.model").read())
             self._unit = scene_3mf.getUnit()
             for node in scene_3mf.getSceneNodes():
diff --git a/plugins/ChangeLogPlugin/ChangeLog.txt b/plugins/ChangeLogPlugin/ChangeLog.txt
index 8da415df05..aefeb92ce5 100755
--- a/plugins/ChangeLogPlugin/ChangeLog.txt
+++ b/plugins/ChangeLogPlugin/ChangeLog.txt
@@ -1,4 +1,9 @@
-
+[3.4.1]
+*Bug fixes
+- Fixed an issue that would occasionally cause an unnecessary extra skin wall to be printed, which increased print time.
+- Fixed an issue in which supports were not generated on the initial layer, because the engine expected a brim to be in place.
+- Conical and tree supports are now limited within the build plate volume.
+- Fixed various startup crashes, including: copying of the version folder, errors while deleting packages, storing the old files, and losing data on install.
 
 [3.4.0]
 
diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index e7dca2ae3e..2b3c2b29f8 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -21,6 +21,7 @@ from UM.Scene.Iterator.DepthFirstIterator import DepthFirstIterator
 from UM.Settings.Interfaces import DefinitionContainerInterface
 from UM.Settings.SettingInstance import SettingInstance #For typing.
 from UM.Tool import Tool #For typing.
+from UM.Mesh.MeshData import MeshData #For typing.
 
 from cura.CuraApplication import CuraApplication
 from cura.Settings.ExtruderManager import ExtruderManager
@@ -62,15 +63,15 @@ class CuraEngineBackend(QObject, Backend):
         if Platform.isLinux() and not default_engine_location:
             if not os.getenv("PATH"):
                 raise OSError("There is something wrong with your Linux installation.")
-            for pathdir in os.getenv("PATH").split(os.pathsep):
+            for pathdir in cast(str, os.getenv("PATH")).split(os.pathsep):
                 execpath = os.path.join(pathdir, executable_name)
                 if os.path.exists(execpath):
                     default_engine_location = execpath
                     break
 
         self._application = CuraApplication.getInstance() #type: CuraApplication
-        self._multi_build_plate_model = None #type: MultiBuildPlateModel
-        self._machine_error_checker = None #type: MachineErrorChecker
+        self._multi_build_plate_model = None #type: Optional[MultiBuildPlateModel]
+        self._machine_error_checker = None #type: Optional[MachineErrorChecker]
 
         if not default_engine_location:
             raise EnvironmentError("Could not find CuraEngine")
@@ -120,7 +121,7 @@ class CuraEngineBackend(QObject, Backend):
         self._engine_is_fresh = True #type: bool # Is the newly started engine used before or not?
 
         self._backend_log_max_lines = 20000 #type: int # Maximum number of lines to buffer
-        self._error_message = None #type: Message # Pop-up message that shows errors.
+        self._error_message = None #type: Optional[Message] # Pop-up message that shows errors.
         self._last_num_objects = defaultdict(int) #type: Dict[int, int] # Count number of objects to see if there is something changed
         self._postponed_scene_change_sources = [] #type: List[SceneNode] # scene change is postponed (by a tool)
 
@@ -145,7 +146,9 @@ class CuraEngineBackend(QObject, Backend):
         self._multi_build_plate_model = self._application.getMultiBuildPlateModel()
 
         self._application.getController().activeViewChanged.connect(self._onActiveViewChanged)
-        self._multi_build_plate_model.activeBuildPlateChanged.connect(self._onActiveViewChanged)
+
+        if self._multi_build_plate_model:
+            self._multi_build_plate_model.activeBuildPlateChanged.connect(self._onActiveViewChanged)
 
         self._application.globalContainerStackChanged.connect(self._onGlobalStackChanged)
         self._onGlobalStackChanged()
@@ -246,7 +249,7 @@ class CuraEngineBackend(QObject, Backend):
         if self._application.getPrintInformation() and build_plate_to_be_sliced == active_build_plate:
             self._application.getPrintInformation().setToZeroPrintInformation(build_plate_to_be_sliced)
 
-        if self._process is None:
+        if self._process is None: # type: ignore
             self._createSocket()
         self.stopSlicing()
         self._engine_is_fresh = False  # Yes we're going to use the engine
@@ -284,12 +287,12 @@ class CuraEngineBackend(QObject, Backend):
         if self._application.getUseExternalBackend():
             return
 
-        if self._process is not None:
+        if self._process is not None: # type: ignore
             Logger.log("d", "Killing engine process")
             try:
-                self._process.terminate()
-                Logger.log("d", "Engine process is killed. Received return code %s", self._process.wait())
-                self._process = None
+                self._process.terminate() # type: ignore
+                Logger.log("d", "Engine process is killed. Received return code %s", self._process.wait()) # type: ignore
+                self._process = None # type: ignore
 
             except Exception as e:  # terminating a process that is already terminating causes an exception, silently ignore this.
                 Logger.log("d", "Exception occurred while trying to kill the engine %s", str(e))
@@ -328,6 +331,9 @@ class CuraEngineBackend(QObject, Backend):
 
         if job.getResult() == StartJobResult.SettingError:
             if self._application.platformActivity:
+                if not self._global_container_stack:
+                    Logger.log("w", "Global container stack not assigned to CuraEngineBackend!")
+                    return
                 extruders = list(ExtruderManager.getInstance().getMachineExtruders(self._global_container_stack.getId()))
                 error_keys = [] #type: List[str]
                 for extruder in extruders:
@@ -361,6 +367,9 @@ class CuraEngineBackend(QObject, Backend):
                 if not stack:
                     continue
                 for key in stack.getErrorKeys():
+                    if not self._global_container_stack:
+                        Logger.log("e", "CuraEngineBackend does not have global_container_stack assigned.")
+                        continue
                     definition = cast(DefinitionContainerInterface, self._global_container_stack.getBottom()).findDefinitions(key = key)
                     if not definition:
                         Logger.log("e", "When checking settings for errors, unable to find definition for key {key} in per-object stack.".format(key = key))
@@ -409,7 +418,8 @@ class CuraEngineBackend(QObject, Backend):
         # Notify the user that it's now up to the backend to do it's job
         self.backendStateChange.emit(BackendState.Processing)
 
-        Logger.log("d", "Sending slice message took %s seconds", time() - self._slice_start_time )
+        if self._slice_start_time:
+            Logger.log("d", "Sending slice message took %s seconds", time() - self._slice_start_time )
 
     ##  Determine enable or disable auto slicing. Return True for enable timer and False otherwise.
     #   It disables when
@@ -476,15 +486,12 @@ class CuraEngineBackend(QObject, Backend):
         else:
             # we got a single scenenode
             if not source.callDecoration("isGroup"):
-                if source.getMeshData() is None:
-                    return
-                if source.getMeshData().getVertices() is None:
+                mesh_data = source.getMeshData()
+                if mesh_data and mesh_data.getVertices() is None:
                     return
 
             build_plate_changed.add(source_build_plate_number)
 
-        build_plate_changed.discard(None)
-        build_plate_changed.discard(-1)  # object not on build plate
         if not build_plate_changed:
             return
 
@@ -577,9 +584,10 @@ class CuraEngineBackend(QObject, Backend):
     #
     #   \param message The protobuf message containing sliced layer data.
     def _onOptimizedLayerMessage(self, message: Arcus.PythonMessage) -> None:
-        if self._start_slice_job_build_plate not in self._stored_optimized_layer_data:
-            self._stored_optimized_layer_data[self._start_slice_job_build_plate] = []
-        self._stored_optimized_layer_data[self._start_slice_job_build_plate].append(message)
+        if self._start_slice_job_build_plate:
+            if self._start_slice_job_build_plate not in self._stored_optimized_layer_data:
+                self._stored_optimized_layer_data[self._start_slice_job_build_plate] = []
+            self._stored_optimized_layer_data[self._start_slice_job_build_plate].append(message)
 
     ##  Called when a progress message is received from the engine.
     #
@@ -619,7 +627,8 @@ class CuraEngineBackend(QObject, Backend):
             gcode_list[index] = replaced
 
         self._slicing = False
-        Logger.log("d", "Slicing took %s seconds", time() - self._slice_start_time )
+        if self._slice_start_time:
+            Logger.log("d", "Slicing took %s seconds", time() - self._slice_start_time )
         Logger.log("d", "Number of models per buildplate: %s", dict(self._numObjectsPerBuildPlate()))
 
         # See if we need to process the sliced layers job.
@@ -658,7 +667,11 @@ class CuraEngineBackend(QObject, Backend):
     ##  Creates a new socket connection.
     def _createSocket(self, protocol_file: str = None) -> None:
         if not protocol_file:
-            protocol_file = os.path.abspath(os.path.join(PluginRegistry.getInstance().getPluginPath(self.getPluginId()), "Cura.proto"))
+            plugin_path = PluginRegistry.getInstance().getPluginPath(self.getPluginId())
+            if not plugin_path:
+                Logger.log("e", "Could not get plugin path!", self.getPluginId())
+                return
+            protocol_file = os.path.abspath(os.path.join(plugin_path, "Cura.proto"))
         super()._createSocket(protocol_file)
         self._engine_is_fresh = True
 
@@ -773,9 +786,9 @@ class CuraEngineBackend(QObject, Backend):
     #   We should reset our state and start listening for new connections.
     def _onBackendQuit(self) -> None:
         if not self._restart:
-            if self._process:
-                Logger.log("d", "Backend quit with return code %s. Resetting process and socket.", self._process.wait())
-                self._process = None
+            if self._process: # type: ignore
+                Logger.log("d", "Backend quit with return code %s. Resetting process and socket.", self._process.wait()) # type: ignore
+                self._process = None # type: ignore
 
     ##  Called when the global container stack changes
     def _onGlobalStackChanged(self) -> None:
@@ -831,6 +844,9 @@ class CuraEngineBackend(QObject, Backend):
             self._change_timer.start()
 
     def _extruderChanged(self) -> None:
+        if not self._multi_build_plate_model:
+            Logger.log("w", "CuraEngineBackend does not have multi_build_plate_model assigned!")
+            return
         for build_plate_number in range(self._multi_build_plate_model.maxBuildPlate + 1):
             if build_plate_number not in self._build_plates_to_be_sliced:
                 self._build_plates_to_be_sliced.append(build_plate_number)
diff --git a/plugins/CuraEngineBackend/StartSliceJob.py b/plugins/CuraEngineBackend/StartSliceJob.py
index 20c426209f..9a40445a18 100644
--- a/plugins/CuraEngineBackend/StartSliceJob.py
+++ b/plugins/CuraEngineBackend/StartSliceJob.py
@@ -5,7 +5,7 @@ import numpy
 from string import Formatter
 from enum import IntEnum
 import time
-from typing import Any, Dict, List, Optional, Set
+from typing import Any, cast, Dict, List, Optional, Set
 import re
 import Arcus #For typing.
 
@@ -209,12 +209,15 @@ class StartSliceJob(Job):
                 if temp_list:
                     object_groups.append(temp_list)
 
-            extruders_enabled = {position: stack.isEnabled for position, stack in CuraApplication.getInstance().getGlobalContainerStack().extruders.items()}
+            global_stack = CuraApplication.getInstance().getGlobalContainerStack()
+            if not global_stack:
+                return
+            extruders_enabled = {position: stack.isEnabled for position, stack in global_stack.extruders.items()}
             filtered_object_groups = []
             has_model_with_disabled_extruders = False
             associated_disabled_extruders = set()
             for group in object_groups:
-                stack = CuraApplication.getInstance().getGlobalContainerStack()
+                stack = global_stack
                 skip_group = False
                 for node in group:
                     extruder_position = node.callDecoration("getActiveExtruderPosition")
@@ -227,7 +230,7 @@ class StartSliceJob(Job):
 
             if has_model_with_disabled_extruders:
                 self.setResult(StartJobResult.ObjectsWithDisabledExtruder)
-                associated_disabled_extruders = [str(c) for c in sorted([int(p) + 1 for p in associated_disabled_extruders])]
+                associated_disabled_extruders = {str(c) for c in sorted([int(p) + 1 for p in associated_disabled_extruders])}
                 self.setMessage(", ".join(associated_disabled_extruders))
                 return
 
@@ -318,7 +321,7 @@ class StartSliceJob(Job):
     #   \param default_extruder_nr Stack nr to use when no stack nr is specified, defaults to the global stack
     def _expandGcodeTokens(self, value: str, default_extruder_nr: int = -1) -> str:
         if not self._all_extruders_settings:
-            global_stack = CuraApplication.getInstance().getGlobalContainerStack()
+            global_stack = cast(ContainerStack, CuraApplication.getInstance().getGlobalContainerStack())
 
             # NB: keys must be strings for the string formatter
             self._all_extruders_settings = {
diff --git a/plugins/GCodeReader/FlavorParser.py b/plugins/GCodeReader/FlavorParser.py
index 990bd98fb5..10f841fc43 100644
--- a/plugins/GCodeReader/FlavorParser.py
+++ b/plugins/GCodeReader/FlavorParser.py
@@ -286,6 +286,7 @@ class FlavorParser:
         self._cancelled = False
         # We obtain the filament diameter from the selected extruder to calculate line widths
         global_stack = CuraApplication.getInstance().getGlobalContainerStack()
+        
         if not global_stack:
             return None
 
diff --git a/plugins/PostProcessingPlugin/scripts/PauseAtHeight.py b/plugins/PostProcessingPlugin/scripts/PauseAtHeight.py
index 545db24048..6354dd4f04 100644
--- a/plugins/PostProcessingPlugin/scripts/PauseAtHeight.py
+++ b/plugins/PostProcessingPlugin/scripts/PauseAtHeight.py
@@ -266,8 +266,10 @@ class PauseAtHeight(Script):
                     # Retraction
                     prepend_gcode += self.putValue(M = 83) + "\n"
                     if retraction_amount != 0:
-                        if firmware_retract:
-                            prepend_gcode += self.putValue(G = 10)
+                        if firmware_retract: #Can't set the distance directly to what the user wants. We have to choose ourselves.
+                            retraction_count = 1 if control_temperatures else 3 #Retract more if we don't control the temperature.
+                            for i in range(retraction_count):
+                                prepend_gcode += self.putValue(G = 10) + "\n"
                         else:
                             prepend_gcode += self.putValue(G = 1, E = -retraction_amount, F = retraction_speed * 60) + "\n"
 
@@ -309,8 +311,10 @@ class PauseAtHeight(Script):
                     prepend_gcode += self.putValue(G = 1, Z = current_z + 1, F = 300) + "\n"
                     prepend_gcode += self.putValue(G = 1, X = x, Y = y, F = 9000) + "\n"
                     if retraction_amount != 0:
-                        if firmware_retract:
-                            prepend_gcode += self.putValue(G = 11)
+                        if firmware_retract: #Can't set the distance directly to what the user wants. We have to choose ourselves.
+                            retraction_count = 1 if control_temperatures else 3 #Retract more if we don't control the temperature.
+                            for i in range(retraction_count):
+                                prepend_gcode += self.putValue(G = 11) + "\n"
                         else:
                             prepend_gcode += self.putValue(G = 1, E = retraction_amount, F = retraction_speed * 60) + "\n"
                     prepend_gcode += self.putValue(G = 1, F = 9000) + "\n"
diff --git a/plugins/RemovableDriveOutputDevice/WindowsRemovableDrivePlugin.py b/plugins/RemovableDriveOutputDevice/WindowsRemovableDrivePlugin.py
index 7a3e1ab5c1..51b6a70b7a 100644
--- a/plugins/RemovableDriveOutputDevice/WindowsRemovableDrivePlugin.py
+++ b/plugins/RemovableDriveOutputDevice/WindowsRemovableDrivePlugin.py
@@ -11,7 +11,7 @@ from UM.i18n import i18nCatalog
 catalog = i18nCatalog("cura")
 
 # Ignore windows error popups. Fixes the whole "Can't open drive X" when user has an SD card reader.
-ctypes.windll.kernel32.SetErrorMode(1)
+ctypes.windll.kernel32.SetErrorMode(1) #type: ignore
 
 # WinAPI Constants that we need
 # Hardcoded here due to stupid WinDLL stuff that does not give us access to these values.
@@ -29,7 +29,7 @@ OPEN_EXISTING = 3 # [CodeStyle: Windows Enum value]
 
 # Setup the DeviceIoControl function arguments and return type.
 # See ctypes documentation for details on how to call C functions from python, and why this is important.
-ctypes.windll.kernel32.DeviceIoControl.argtypes = [
+ctypes.windll.kernel32.DeviceIoControl.argtypes = [ #type: ignore
     wintypes.HANDLE,                    # _In_          HANDLE hDevice
     wintypes.DWORD,                     # _In_          DWORD dwIoControlCode
     wintypes.LPVOID,                    # _In_opt_      LPVOID lpInBuffer
@@ -39,7 +39,7 @@ ctypes.windll.kernel32.DeviceIoControl.argtypes = [
     ctypes.POINTER(wintypes.DWORD),     # _Out_opt_     LPDWORD lpBytesReturned
     wintypes.LPVOID                     # _Inout_opt_   LPOVERLAPPED lpOverlapped
 ]
-ctypes.windll.kernel32.DeviceIoControl.restype = wintypes.BOOL
+ctypes.windll.kernel32.DeviceIoControl.restype = wintypes.BOOL #type: ignore
 
 
 ## Removable drive support for windows
diff --git a/plugins/SliceInfoPlugin/SliceInfo.py b/plugins/SliceInfoPlugin/SliceInfo.py
index fe17af89eb..2e9e557c4a 100755
--- a/plugins/SliceInfoPlugin/SliceInfo.py
+++ b/plugins/SliceInfoPlugin/SliceInfo.py
@@ -16,7 +16,7 @@ from UM.i18n import i18nCatalog
 from UM.Logger import Logger
 from UM.PluginRegistry import PluginRegistry
 from UM.Qt.Duration import DurationFormat
-
+from typing import cast, Optional
 from .SliceInfoJob import SliceInfoJob
 
 
@@ -79,11 +79,16 @@ class SliceInfo(QObject, Extension):
         return dialog
 
     @pyqtSlot(result = str)
-    def getExampleData(self) -> str:
+    def getExampleData(self) -> Optional[str]:
         if self._example_data_content is None:
-            file_path = os.path.join(PluginRegistry.getInstance().getPluginPath(self.getPluginId()), "example_data.json")
-            with open(file_path, "r", encoding = "utf-8") as f:
-                self._example_data_content = f.read()
+            plugin_path = PluginRegistry.getInstance().getPluginPath(self.getPluginId())
+            if not plugin_path:
+                Logger.log("e", "Could not get plugin path!", self.getPluginId())
+                return None
+            file_path = os.path.join(plugin_path, "example_data.json")
+            if file_path:
+                with open(file_path, "r", encoding = "utf-8") as f:
+                    self._example_data_content = f.read()
         return self._example_data_content
 
     @pyqtSlot(bool)
diff --git a/plugins/Toolbox/src/Toolbox.py b/plugins/Toolbox/src/Toolbox.py
index 4e59fcd055..3fec67c96e 100644
--- a/plugins/Toolbox/src/Toolbox.py
+++ b/plugins/Toolbox/src/Toolbox.py
@@ -6,7 +6,7 @@ import json
 import os
 import tempfile
 import platform
-from typing import List
+from typing import cast, List
 
 from PyQt5.QtCore import QUrl, QObject, pyqtProperty, pyqtSignal, pyqtSlot
 from PyQt5.QtNetwork import QNetworkAccessManager, QNetworkRequest, QNetworkReply
@@ -250,7 +250,10 @@ class Toolbox(QObject, Extension):
         if not plugin_path:
             return None
         path = os.path.join(plugin_path, "resources", "qml", qml_name)
+        
         dialog = self._application.createQmlComponent(path, {"toolbox": self})
+        if not dialog:
+            raise Exception("Failed to create toolbox dialog")
         return dialog
 
     def _convertPluginMetadata(self, plugin: Dict[str, Any]) -> Dict[str, Any]:
diff --git a/plugins/UM3NetworkPrinting/ClusterUM3OutputDevice.py b/plugins/UM3NetworkPrinting/ClusterUM3OutputDevice.py
index 757ed4ef66..84e0a66170 100644
--- a/plugins/UM3NetworkPrinting/ClusterUM3OutputDevice.py
+++ b/plugins/UM3NetworkPrinting/ClusterUM3OutputDevice.py
@@ -1,7 +1,7 @@
 # Copyright (c) 2018 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
-from typing import Any, cast, Set, Tuple, Union
+from typing import Any, cast, Optional, Set, Tuple, Union
 
 from UM.FileHandler.FileHandler import FileHandler
 from UM.FileHandler.FileWriter import FileWriter #To choose based on the output file mode (text vs. binary).
@@ -9,6 +9,7 @@ from UM.FileHandler.WriteFileJob import WriteFileJob #To call the file writer as
 from UM.Logger import Logger
 from UM.Settings.ContainerRegistry import ContainerRegistry
 from UM.i18n import i18nCatalog
+from UM.Mesh.MeshWriter import MeshWriter # For typing
 from UM.Message import Message
 from UM.Qt.Duration import Duration, DurationFormat
 from UM.OutputDevice import OutputDeviceError #To show that something went wrong when writing.
@@ -104,10 +105,11 @@ class ClusterUM3OutputDevice(NetworkedPrinterOutputDevice):
             file_formats = CuraApplication.getInstance().getMeshFileHandler().getSupportedFileTypesWrite()
 
         global_stack = CuraApplication.getInstance().getGlobalContainerStack()
+        #Create a list from the supported file formats string.
         if not global_stack:
+            Logger.log("e", "Missing global stack!")
             return
 
-        #Create a list from the supported file formats string.
         machine_file_formats = global_stack.getMetaDataEntry("file_formats").split(";")
         machine_file_formats = [file_type.strip() for file_type in machine_file_formats]
         #Exception for UM3 firmware version >=4.4: UFP is now supported and should be the preferred file format.
@@ -134,6 +136,9 @@ class ClusterUM3OutputDevice(NetworkedPrinterOutputDevice):
             return
 
         #This function pauses with the yield, waiting on instructions on which printer it needs to print with.
+        if not writer:
+            Logger.log("e", "Missing file or mesh writer!")
+            return
         self._sending_job = self._sendPrintJob(writer, preferred_format, nodes)
         self._sending_job.send(None) #Start the generator.
 
@@ -213,16 +218,14 @@ class ClusterUM3OutputDevice(NetworkedPrinterOutputDevice):
         yield #To prevent having to catch the StopIteration exception.
 
     def _sendPrintJobWaitOnWriteJobFinished(self, job: WriteFileJob) -> None:
-        # This is the callback when the job finishes, where the message is created
-        assert(self._write_job_progress_message is not None)
-        self._write_job_progress_message.hide()
+        if self._write_job_progress_message:
+            self._write_job_progress_message.hide()
 
         self._progress_message = Message(i18n_catalog.i18nc("@info:status", "Sending data to printer"), lifetime = 0, dismissable = False, progress = -1,
                                          title = i18n_catalog.i18nc("@info:title", "Sending Data"))
         self._progress_message.addAction("Abort", i18n_catalog.i18nc("@action:button", "Cancel"), icon = None, description = "")
         self._progress_message.actionTriggered.connect(self._progressMessageActionTriggered)
         self._progress_message.show()
-
         parts = []
 
         target_printer, preferred_format, stream = self._dummy_lambdas
@@ -259,7 +262,7 @@ class ClusterUM3OutputDevice(NetworkedPrinterOutputDevice):
             self.activePrinterChanged.emit()
 
     def _onPostPrintJobFinished(self, reply: QNetworkReply) -> None:
-        if self._progress_message is not None:
+        if self._progress_message:
             self._progress_message.hide()
         self._compressing_gcode = False
         self._sending_gcode = False
diff --git a/plugins/UM3NetworkPrinting/DiscoverUM3Action.py b/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
index 3752cc0c25..b48a57e0a2 100644
--- a/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
+++ b/plugins/UM3NetworkPrinting/DiscoverUM3Action.py
@@ -3,7 +3,7 @@
 
 import os.path
 import time
-from typing import Optional
+from typing import cast, Optional
 
 from PyQt5.QtCore import pyqtSignal, pyqtProperty, pyqtSlot, QObject
 
diff --git a/plugins/USBPrinting/USBPrinterOutputDevice.py b/plugins/USBPrinting/USBPrinterOutputDevice.py
index 69a0ecb40c..f9c6011f7b 100644
--- a/plugins/USBPrinting/USBPrinterOutputDevice.py
+++ b/plugins/USBPrinting/USBPrinterOutputDevice.py
@@ -423,7 +423,7 @@ class USBPrinterOutputDevice(PrinterOutputDevice):
         elapsed_time = int(time() - self._print_start_time)
         print_job = self._printers[0].activePrintJob
         if print_job is None:
-            print_job = PrintJobOutputModel(output_controller = GenericOutputController(self), name= Application.getInstance().getPrintInformation().jobName)
+            print_job = PrintJobOutputModel(output_controller = GenericOutputController(self), name= CuraApplication.getInstance().getPrintInformation().jobName)
             print_job.updateState("printing")
             self._printers[0].updateActivePrintJob(print_job)
 
diff --git a/plugins/VersionUpgrade/VersionUpgrade34to40/VersionUpgrade34to40.py b/plugins/VersionUpgrade/VersionUpgrade34to40/VersionUpgrade34to40.py
index 2877985921..0cf7ef0cc4 100644
--- a/plugins/VersionUpgrade/VersionUpgrade34to40/VersionUpgrade34to40.py
+++ b/plugins/VersionUpgrade/VersionUpgrade34to40/VersionUpgrade34to40.py
@@ -71,6 +71,8 @@ class VersionUpgrade34to40(VersionUpgrade):
         self._resetConcentric3DInfillPattern(parser)
         if "values" in parser:
             for deleted_setting in deleted_settings:
+                if deleted_setting not in parser["values"]:
+                    continue
                 del parser["values"][deleted_setting]
 
         result = io.StringIO()
diff --git a/resources/definitions/raise3D_N2_plus_single.def.json b/resources/definitions/raise3D_N2_plus_single.def.json
index 55b8c9c8c5..b829147160 100644
--- a/resources/definitions/raise3D_N2_plus_single.def.json
+++ b/resources/definitions/raise3D_N2_plus_single.def.json
@@ -67,7 +67,7 @@
         },
         "machine_start_gcode": {
             "default_value": "G90\nG21\n; home all axes\nG28\nG92 X0 Y0 Z0\n; move heatbed into position\nG1 X20.0 Y20.0 Z1.0 F1000\n; zero extruders\nG92 E0 E1\nT0; right tool\n; set extruder steps per mm\nM92 E140\n; purge nozzle\nG1 E25 F250\n; zero extruders\nG92 E0 E1\n; move heatbed down a little more\nG1 Z5.0 F20\n; wait 600ms\nG4 600\n; move to tack down the strands\nG1 X20.0 Y30.0 Z0 F9000\n; wait 600ms\nG4 600\n;move up a bit\nG1 Z5.0 F9000\n; wait 300ms\nG4 300\n;fast move to center\nG1 X152.5 Y152.5 F9000\nT0\n;Raise3D Job Start\nM117 Printing…\nM1001\n"
-	},
+        },
         "machine_end_gcode": {
             "default_value": "M107\nM1002\nM104 S0 T1\nM104 S0 T0\nM140 S0\nM117 Print Complete.\nG28 X0 Y0\nG91\nG1 Z10\nG90\nM84"
         },
diff --git a/resources/qml/Preferences/MaterialView.qml b/resources/qml/Preferences/MaterialView.qml
index ad91f2ee9a..bab0b703d2 100644
--- a/resources/qml/Preferences/MaterialView.qml
+++ b/resources/qml/Preferences/MaterialView.qml
@@ -515,7 +515,7 @@ TabView
         if(entry_name in materialPreferenceValues[material_guid] && materialPreferenceValues[material_guid][entry_name] == new_value)
         {
             // value has not changed
-            return
+            return;
         }
         materialPreferenceValues[material_guid][entry_name] = new_value;
 
@@ -529,30 +529,35 @@ TabView
         {
             return materialPreferenceValues[material_guid][entry_name];
         }
-        return 0;
+
+        var material_weight = Cura.ContainerManager.getContainerMetaDataEntry(base.containerId, "properties", "weight");
+        return material_weight || 0;
     }
 
     // update the display name of the material
-    function updateMaterialDisplayName (old_name, new_name) {
+    function updateMaterialDisplayName (old_name, new_name)
+    {
         // don't change when new name is the same
         if (old_name == new_name) {
-            return
+            return;
         }
 
         // update the values
-        base.materialManager.setMaterialName(base.currentMaterialNode, new_name)
-        materialProperties.name = new_name
+        base.materialManager.setMaterialName(base.currentMaterialNode, new_name);
+        materialProperties.name = new_name;
     }
 
     // update the type of the material
-    function updateMaterialType (old_type, new_type) {
-        base.setMetaDataEntry("material", old_type, new_type)
-        materialProperties.material= new_type
+    function updateMaterialType (old_type, new_type)
+    {
+        base.setMetaDataEntry("material", old_type, new_type);
+        materialProperties.material= new_type;
     }
 
     // update the brand of the material
-    function updateMaterialBrand (old_brand, new_brand) {
-        base.setMetaDataEntry("brand", old_brand, new_brand)
-        materialProperties.brand = new_brand
+    function updateMaterialBrand (old_brand, new_brand)
+    {
+        base.setMetaDataEntry("brand", old_brand, new_brand);
+        materialProperties.brand = new_brand;
     }
 }
diff --git a/resources/qml/SidebarHeader.qml b/resources/qml/SidebarHeader.qml
index cf199fd12b..0e5ac852e8 100644
--- a/resources/qml/SidebarHeader.qml
+++ b/resources/qml/SidebarHeader.qml
@@ -408,7 +408,7 @@ Column
                 {
                     return false;
                 }
-                return Cura.ContainerManager.getContainerMetaDataEntry(activeExtruder.material.id, "compatible") == "True"
+                return Cura.ContainerManager.getContainerMetaDataEntry(activeExtruder.material.id, "compatible", "") == "True"
             }
         }
     }
diff --git a/run_mypy.py b/run_mypy.py
index 2a2c72dbbe..27f07cd281 100644
--- a/run_mypy.py
+++ b/run_mypy.py
@@ -1,16 +1,32 @@
-#!env python
+#!/usr/bin/env python
 import os
 import sys
 import subprocess
 
+
 # A quick Python implementation of unix 'where' command.
-def where(exeName, searchPath=os.getenv("PATH")):
-    paths = searchPath.split(";" if sys.platform == "win32" else ":")
-    for path in paths:
-        candidatePath = os.path.join(path, exeName)
-        if os.path.exists(candidatePath):
-            return candidatePath
-    return None
+def where(exe_name: str, search_path: str = os.getenv("PATH")) -> str:
+    if search_path is None:
+        search_path = ""
+    paths = search_path.split(os.pathsep)
+    result = ""
+    print("  ->  sys.executable location: %s" % sys.executable)
+    sys_exec_dir = os.path.dirname(sys.executable)
+    root_dir = os.path.dirname(sys_exec_dir)
+    paths += [sys_exec_dir,
+              os.path.join(root_dir, "bin"),
+              os.path.join(root_dir, "scripts"),
+              ]
+    paths = set(paths)
+
+    for path in sorted(paths):
+        print(" -> Searching %s" % path)
+        candidate_path = os.path.join(path, exe_name)
+        if os.path.exists(candidate_path):
+            result = candidate_path
+            break
+    return result
+
 
 def findModules(path):
     result = []
@@ -19,6 +35,7 @@ def findModules(path):
             result.append(entry.name)
     return result
 
+
 def main():
     # Find Uranium via the PYTHONPATH var
     uraniumUMPath = where("UM", os.getenv("PYTHONPATH"))
@@ -26,16 +43,19 @@ def main():
         uraniumUMPath = os.path.join("..", "Uranium")
     uraniumPath = os.path.dirname(uraniumUMPath)
 
-    mypyPathParts = [".", os.path.join(".", "plugins"), os.path.join(".", "plugins", "VersionUpgrade"),
-                     uraniumPath, os.path.join(uraniumPath, "stubs")]
+    mypy_path_parts = [".", os.path.join(".", "plugins"), os.path.join(".", "plugins", "VersionUpgrade"),
+                       uraniumPath, os.path.join(uraniumPath, "stubs")]
     if sys.platform == "win32":
-        os.putenv("MYPYPATH", ";".join(mypyPathParts))
+        os.putenv("MYPYPATH", ";".join(mypy_path_parts))
     else:
-        os.putenv("MYPYPATH", ":".join(mypyPathParts))
+        os.putenv("MYPYPATH", ":".join(mypy_path_parts))
 
     # Mypy really needs to be run via its Python script otherwise it can't find its data files.
-    mypyExe = where("mypy.bat" if sys.platform == "win32" else "mypy")
-    mypyModule = os.path.join(os.path.dirname(mypyExe), "mypy")
+    mypy_exe_name = "mypy.exe" if sys.platform == "win32" else "mypy"
+    mypy_exe_dir = where(mypy_exe_name)
+    mypy_module = os.path.join(os.path.dirname(mypy_exe_dir), mypy_exe_name)
+    print("Found mypy exe path: %s" % mypy_exe_dir)
+    print("Found mypy module path: %s" % mypy_module)
 
     plugins = findModules("plugins")
     plugins.sort()
@@ -44,11 +64,17 @@ def main():
 
     for mod in mods:
         print("------------- Checking module {mod}".format(**locals()))
-        result = subprocess.run([sys.executable, mypyModule, "-p", mod, "--ignore-missing-imports"])
+        if sys.platform == "win32":
+            result = subprocess.run([mypy_module, "-p", mod, "--ignore-missing-imports"])
+        else:
+            result = subprocess.run([sys.executable, mypy_module, "-p", mod, "--ignore-missing-imports"])
         if result.returncode != 0:
             print("\nModule {mod} failed checking. :(".format(**locals()))
             return 1
     else:
         print("\n\nDone checking. All is good.")
     return 0
-sys.exit(main())
+
+
+if __name__ == "__main__":
+    sys.exit(main())