Thanks for your reply. I knew this crash was triggered by unbalanced call to dispatch_group_leave() ,but I have checked all call to dispatch_group_leave in my project, but there are not unbalanced call. I collected this crash by Firebase Crashlytics and I can't reproduce it by myself. Firebase Crashlytics does't provide Apple crash report.Firebase Crashlytics only provides all call stack in every thread. I also tried to search this crash in Xcode Crashes organizer, but there was not. Please, can I do anything else to help you locate the crash ?

I encountered the same problem.This crash only apears above iOS14,including iOS15.There is no such case in versions below iOS 14 too And there is not frame about the function of my app on the top of the crashed stack trace.So I can hardly find why this crash happends. Crashed: com.apple.main-thread 0 libdispatch.dylib 0x19b7b87b8 dispatch_group_leave.cold.1 + 36 1 libdispatch.dylib 0x19b784638 _dispatch_group_wake + 138 2 libdispatch.dylib 0x19b781a54 _dispatch_call_block_and_release + 32 3 libdispatch.dylib 0x19b7837ec _dispatch_client_callout + 20 4 libdispatch.dylib 0x19b791c40 _dispatch_main_queue_callback_4CF + 884 5 CoreFoundation 0x19bb101f8 CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 16 6 CoreFoundation 0x19bb0a0d0 __CFRunLoopRun + 2524 7 CoreFoundation 0x19bb091c0 CFRunLoopRunSpecific + 600 8 GraphicsServices 0x1b30f1734 GSEventRunModal + 164 9 UIKitCore 0x19e5777e4 -[UIApplication _run] + 1072 10 UIKitCore 0x19e57d054 UIApplicationMain + 168 11 MyApp 0x1022eae98 main + 22 (main.m:22) 12 libdyld.dylib 0x19b7c5cf8 start + 4

I encountered the same problem.This crash only apears above iOS14,including iOS15.There is no such case in versions below iOS 14 too And there is not frame about the function of my app on the top of the crashed stack trace.So I can hardly find why this crash happends. Crashed: com.apple.main-thread 0 libdispatch.dylib 0x19b7b87b8 dispatch_group_leave.cold.1 + 36 1 libdispatch.dylib 0x19b784638 _dispatch_group_wake + 138 2 libdispatch.dylib 0x19b781a54 _dispatch_call_block_and_release + 32 3 libdispatch.dylib 0x19b7837ec _dispatch_client_callout + 20 4 libdispatch.dylib 0x19b791c40 _dispatch_main_queue_callback_4CF + 884 5 CoreFoundation 0x19bb101f8 CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE + 16 6 CoreFoundation 0x19bb0a0d0 __CFRunLoopRun + 2524 7 CoreFoundation 0x19bb091c0 CFRunLoopRunSpecific + 600 8 GraphicsServices 0x1b30f1734 GSEventRunModal + 164 9 UIKitCore 0x19e5777e4 -[UIApplication _run] + 1072 10 UIKitCore 0x19e57d054 UIApplicationMain + 168 11 MyApp 0x1022eae98 main + 22 (main.m:22) 12 libdyld.dylib 0x19b7c5cf8 start + 4