The microwave system would update UserInterface on any container changed instead of just the microwave_entity_container. This would cause it to error when trying to update the UI when ConstructionSystem inserted the circuit board and components.
private void OnContentUpdate(EntityUid uid, MicrowaveComponent component, ContainerModifiedMessage args) // For some reason ContainerModifiedMessage just can't be used at all with Entity<T>. TODO: replace with Entity<T> syntax once that's possible
{
+ if (component.Storage != args.Container)
+ return;
+
UpdateUserInterfaceState(uid, component);
}