layoutSubviews() fixes the issue, but it definitely looks like a bug (iOS 14.4.1).

I also have a crash report that looks almost exactly the same. More than that, I have two more different crash reports, but all of them have zero Exception Codes and have no "Termination Reason" field. In my case in all those crash reports I have a ton of threads that are waiting for some network operations (some Firestore stuff in my app) so my guess is that it can be related to some resource shortage (memory? descriptors? something related to threading?). But that's just a guess, I may very well be wrong.