We are observing the same issue on an app that was working fine before the latest release of iOS 14.6 For us ,the responsible code is : [NSManagedObjectContext _disposeObjects:count:notifyParent:] which is triggered when a user logs out of the app, and we reset every objects of our CoreData stack. Hope there will be a fix some day, until then, we are going to go down the -com.apple.CoreData.ConcurrencyDebug 1 road and try to nest every CoreData call into a [NSManagedObjectContext performBlockAndWait:] block.