Thanks @kobunketsu. The app I'm working on only uses less than a dozen block based animations. I keep looking for what we've done wrong to trigger it this behaviour, because surely not every app which uses Core Animation is crashing with this regularity. But you are right the crashes started happening in mid October with our Xcode 15 build. What sort of reduction of the crashes did you get from disabling the implicit animations?

Could be. I have run the app against Profiler and checked for leaks but haven't come up with any clues. Ran it through the Static Analyzer, + Running with Main Thread checker, Address Sanitizer, Thread Sanitizer as well Zombie Objects. Again no clues. Nothing that points towards the animations being the cause. I have double checked the half dozen animations I have done in my app, believe that I that they should all be running on the Main Thread.