So we are finally out of this problem. The issue was the CoreData thread violations. Thanks to the community's suggestion, we passed the -com.apple.CoreData.ConcurrencyDebug 1 argument and this helped figuring out all the violations which caused multiple crashes. After adding appropriate concurrency queues to the NSManagedObjectContext, we were able to run the app flawlessly on iOS 15.x.

We are experiencing the same issue. We had deployed an app last year. It's been working fine till the end of November when our client reported crashes on the app since they upgraded to iOS 15.1.1. According to them, the app was working fine on iOS 14.8. For testing purposes, we kept one of our devices to 14.2 and enrolled the other to the 15.2 beta. The results are, the app runs smoothly on 14.2 and even on 15.0. But on 15.1.1 and 15.2, there are crashes and they are mainly caused by NSPersistentStoreCoordinator where we have been dealing with privateConcurrency contexts. The crashes we mainly experience on latest OS say EXC_BAD_ACCESS. I do not know how this is linked with the crashes. Still waiting for some workaround. Anybody facing the same issue??