These really seem like issues with the FliteController implementation in each view controller. The crash is very much a crash of FliteController, and the OpenEarsEventsObserver is a separate object (with very strong separation between the two objects in question) and there’s no reason for it to care whether it has a set delegate and in which view controller it is set or not set.
I think we actually need to just troubleshoot why your FliteController instance doesn’t work quite right. I would shut off OpenEarsEventsObserver entirely (don’t instantiate it, don’t make anything a delegate of it) and see if this crash replicates independently without anything going on but FliteController.