Solved (with an ugly fix) that after loading some projects, 'Slicing...' appears without doing anything. CURA-1263

plugins/3MFReader/WorkspaceDialog.py

@@ -144,6 +144,11 @@ class WorkspaceDialog(QObject):
         if key in self._result:
             self._result[key] = strategy
 
+    ##  Close the backend: otherwise one could end up with "Slicing..."
+    @pyqtSlot()
+    def closeBackend(self):
+        Application.getInstance().getBackend().close()
+
     def setMaterialConflict(self, material_conflict):
         self._has_material_conflict = material_conflict
         self.materialConflictChanged.emit()

plugins/3MFReader/WorkspaceDialog.qml

@@ -305,7 +305,7 @@ UM.Dialog
         {
             id: ok_button
             text: catalog.i18nc("@action:button","OK");
-            onClicked: { manager.onOkButtonClicked() }
+            onClicked: { manager.closeBackend(); manager.onOkButtonClicked() }
             enabled: true
         },
         Button

plugins/CuraEngineBackend/CuraEngineBackend.py

@@ -149,6 +149,7 @@ class CuraEngineBackend(Backend):
 
     ##  Perform a slice of the scene.
     def slice(self):
+        Logger.log("d", "Starting slice job...")
         self._slice_start_time = time()
         if not self._enabled or not self._global_container_stack:  # We shouldn't be slicing.
             # try again in a short time