This happens when the printer is changed, such as when changing the Machine Width in the machine settings dialogue. It updates these menus then and if not all extruders are defined it'll give the following errors:
2020-03-20 16:56:57,839 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/resources/qml/Menus/SettingsMenu.qml:51: TypeError: Cannot read property 'isEnabled' of undefined
2020-03-20 16:56:57,840 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/resources/qml/Menus/SettingsMenu.qml:44: TypeError: Cannot read property 'isEnabled' of undefined
2020-03-20 16:56:57,841 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/resources/qml/Menus/MaterialMenu.qml:26: TypeError: Cannot read property 'isEnabled' of undefined
2020-03-20 16:56:57,841 - WARNING - [MainThread] UM.Qt.QtApplication.__onQmlWarning [406]: file:///home/trin/Gedeeld/Projects/Cura/resources/qml/Menus/MaterialMenu.qml:28: TypeError: Cannot read property 'material' of undefined
Done during Turbo Testing and Tooling.