diff --git a/plugins/CuraEngineBackend/CuraEngineBackend.py b/plugins/CuraEngineBackend/CuraEngineBackend.py
index 935ec94054..98f8473225 100755
--- a/plugins/CuraEngineBackend/CuraEngineBackend.py
+++ b/plugins/CuraEngineBackend/CuraEngineBackend.py
@@ -453,8 +453,9 @@ class CuraEngineBackend(QObject, Backend):
 
     def _onStackErrorCheckFinished(self):
         self._is_error_check_scheduled = False
-        self.needsSlicing()
-        self._onChanged()
+        if self._need_slicing:
+            self.needsSlicing()
+            self._onChanged()
 
     ##  Called when a sliced layer data message is received from the engine.
     #
@@ -611,17 +612,16 @@ class CuraEngineBackend(QObject, Backend):
             if self._process:
                 Logger.log("d", "Backend quit with return code %s. Resetting process and socket.", self._process.wait())
                 self._process = None
-                ##  Called when the global container stack changes
 
+    ##  Called when the global container stack changes
     def _onGlobalStackChanged(self):
         if self._global_container_stack:
             self._global_container_stack.propertyChanged.disconnect(self._onSettingChanged)
             self._global_container_stack.containersChanged.disconnect(self._onChanged)
             extruders = list(ExtruderManager.getInstance().getMachineExtruders(self._global_container_stack.getId()))
 
-            if extruders:
-                for extruder in extruders:
-                    extruder.propertyChanged.disconnect(self._onSettingChanged)
+            for extruder in extruders:
+                extruder.propertyChanged.disconnect(self._onSettingChanged)
 
         self._global_container_stack = Application.getInstance().getGlobalContainerStack()
 
@@ -629,9 +629,8 @@ class CuraEngineBackend(QObject, Backend):
             self._global_container_stack.propertyChanged.connect(self._onSettingChanged)  # Note: Only starts slicing when the value changed.
             self._global_container_stack.containersChanged.connect(self._onChanged)
             extruders = list(ExtruderManager.getInstance().getMachineExtruders(self._global_container_stack.getId()))
-            if extruders:
-                for extruder in extruders:
-                    extruder.propertyChanged.connect(self._onSettingChanged)
+            for extruder in extruders:
+                extruder.propertyChanged.connect(self._onSettingChanged)
             self._onActiveExtruderChanged()
             self._onChanged()
 
@@ -640,9 +639,8 @@ class CuraEngineBackend(QObject, Backend):
             # Connect all extruders of the active machine. This might cause a few connects that have already happend,
             # but that shouldn't cause issues as only new / unique connections are added.
             extruders = list(ExtruderManager.getInstance().getMachineExtruders(self._global_container_stack.getId()))
-            if extruders:
-                for extruder in extruders:
-                    extruder.propertyChanged.connect(self._onSettingChanged)
+            for extruder in extruders:
+                extruder.propertyChanged.connect(self._onSettingChanged)
         if self._active_extruder_stack:
             self._active_extruder_stack.containersChanged.disconnect(self._onChanged)