diff --git a/cura/Machines/MaterialManager.py b/cura/Machines/MaterialManager.py
index 4d9574bf38..160508e7a6 100644
--- a/cura/Machines/MaterialManager.py
+++ b/cura/Machines/MaterialManager.py
@@ -683,7 +683,11 @@ class MaterialManager(QObject):
 
     @pyqtSlot(str)
     def removeFavorite(self, root_material_id: str) -> None:
-        self._favorites.remove(root_material_id)
+        try:
+            self._favorites.remove(root_material_id)
+        except KeyError:
+            Logger.log("w", "Could not delete material %s from favorites as it was already deleted", root_material_id)
+            return
         self.materialsUpdated.emit()
 
         # Ensure all settings are saved.
@@ -692,4 +696,4 @@ class MaterialManager(QObject):
 
     @pyqtSlot()
     def getFavorites(self):
-        return self._favorites
\ No newline at end of file
+        return self._favorites
diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index f12a5b1222..ef0898bb04 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -833,7 +833,10 @@ class CuraEngineBackend(QObject, Backend):
             self._onChanged()
 
     def _onProcessLayersFinished(self, job: ProcessSlicedLayersJob) -> None:
-        del self._stored_optimized_layer_data[job.getBuildPlate()]
+        if job.getBuildPlate() in self._stored_optimized_layer_data:
+            del self._stored_optimized_layer_data[job.getBuildPlate()]
+        else:
+            Logger.log("w", "The optimized layer data was already deleted for buildplate %s", job.getBuildPlate())
         self._process_layers_job = None
         Logger.log("d", "See if there is more to slice(2)...")
         self._invokeSlice()
diff --git a/plugins/FirmwareUpdater/FirmwareUpdaterMachineAction.py b/plugins/FirmwareUpdater/FirmwareUpdaterMachineAction.py
index 0a3e3a0ff0..59552775b6 100644
--- a/plugins/FirmwareUpdater/FirmwareUpdaterMachineAction.py
+++ b/plugins/FirmwareUpdater/FirmwareUpdaterMachineAction.py
@@ -57,7 +57,7 @@ class FirmwareUpdaterMachineAction(MachineAction):
     outputDeviceCanUpdateFirmwareChanged = pyqtSignal()
     @pyqtProperty(QObject, notify = outputDeviceCanUpdateFirmwareChanged)
     def firmwareUpdater(self) -> Optional["FirmwareUpdater"]:
-        if self._active_output_device and self._active_output_device.activePrinter.getController().can_update_firmware:
+        if self._active_output_device and self._active_output_device.activePrinter and self._active_output_device.activePrinter.getController().can_update_firmware:
             self._active_firmware_updater = self._active_output_device.getFirmwareUpdater()
             return self._active_firmware_updater