Long-time lurker, first time poster. I've got a crash that I cannot, for the life of me, make heads or tails of or even attempt to reproduce. According to Firebase, the culprit seems to be a threading violation, which seems simple enough. I've tried using the Main Thread Checker with no luck. I don't know the specific conditions at the time of the crash. Fatal Exception: NSInternalInconsistencyException 0	CoreFoundation								 0x1a3931654 __exceptionPreprocess 1	libobjc.A.dylib								0x1a3653bcc objc_exception_throw 2	CoreFoundation								 0x1a38346ec +[_CFXNotificationTokenRegistration keyCallbacks] 3	Foundation										 0x1a3c7a16c -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] 4	FrontBoardServices						 0x1a8b00e84 -[FBSSerialQueue assertOnQueue] 5	FrontBoardServices						 0x1a8ab6d88 -[FBSSceneImpl updateClientSettings:withTransitionContext:] 6	FrontBoardServices						 0x1a8ab6fe8 -[FBSSceneImpl updateClientSettingsWithTransitionBlock:] 7	FrontBoardServices						 0x1a8ab6ef8 -[FBSSceneImpl updateClientSettingsWithBlock:] 8	UIKitCore											0x1a755c6c0 -[FBSScene(UIApp) updateUIClientSettingsWithBlock:] 9	UIKitCore											0x1a79d9194 -[UIApplication _setAmbiguousControlCenterActivationMargin:] 10 UIKitCore											0x1a783bd24 -[UIPeripheralHost(UIKitInternal) setAmbiguousControlCenterActivationMargin:] 11 UIKitCore											0x1a77cb35c -[UIInputWindowController viewDidLayoutSubviews] 12 UIKitCore											0x1a7e999dc -[UIView(CALayerDelegate) layoutSublayersOfLayer:] 13 QuartzCore										 0x1aa436494 -[CALayer layoutSublayers] 14 QuartzCore										 0x1aa43c5ec CA::Layer::layout_if_needed(CA::Transaction*) 15 QuartzCore										 0x1aa447128 CA::Layer::layout_and_display_if_needed(CA::Transaction*) 16 QuartzCore										 0x1aa38fb44 CA::Context::commit_transaction(CA::Transaction*, double) 17 QuartzCore										 0x1aa3b94e4 CA::Transaction::commit() 18 QuartzCore										 0x1aa3b9ef8 CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) 19 CoreFoundation								 0x1a38aef2c CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION 20 CoreFoundation								 0x1a38a9e20 __CFRunLoopDoObservers 21 CoreFoundation								 0x1a38aa29c __CFRunLoopRun 22 CoreFoundation								 0x1a38a9ba8 CFRunLoopRunSpecific 23 WebCore												0x1abe43ee8 RunWebThread(void*) 24 libsystem_pthread.dylib				0x1a3647d98 _pthread_start 25 libsystem_pthread.dylib				0x1a364b74c thread_start Interestingly enough, it's a web thread that crashed. Crashed: WebThread 0	SwipeKit											 0x104a354c4 FIRCLSProcessRecordAllThreads + 392 (FIRCLSProcess.c:392) 1	SwipeKit											 0x104a358a8 FIRCLSProcessRecordAllThreads + 423 (FIRCLSProcess.c:423) 2	SwipeKit											 0x104a2bdb0 FIRCLSHandler + 34 (FIRCLSHandler.m:34) 3	SwipeKit											 0x104a27878 __FIRCLSExceptionRecord_block_invoke + 218 (FIRCLSException.mm:218) 4	libdispatch.dylib							0x1a35f7524 _dispatch_client_callout + 16 5	libdispatch.dylib							0x1a35db1fc _dispatch_lane_barrier_sync_invoke_and_complete + 56 6	SwipeKit											 0x104a27010 FIRCLSExceptionRecord + 225 (FIRCLSException.mm:225) 7	SwipeKit											 0x104a27308 FIRCLSExceptionRecordNSException + 111 (FIRCLSException.mm:111) 8	SwipeKit											 0x104a26bf0 FIRCLSTerminateHandler() + 279 (FIRCLSException.mm:279) 9	libcabi.dylib								0x1a36fa14c std::terminate(void (*)()) + 16 10 libcabi.dylib								0x1a36fce58 cxa_rethrow + 144 11 libobjc.A.dylib								0x1a3653d80 objc_exception_rethrow + 40 12 CoreFoundation								 0x1a38a9c14 CFRunLoopRunSpecific + 532 13 WebCore												0x1abe43ee8 RunWebThread(void*) + 612 14 libsystem_pthread.dylib				0x1a3647d98 _pthread_start + 156 15 libsystem_pthread.dylib				0x1a364b74c thread_start + 8 I'm hoping that someone can help me make sense of the crash reports and give me some more insight into how i might reproduce and address this issue. Crash reports attached. Crash Report 1 - https://developer.apple.com/forums/content/attachment/f863a752-6569-4677-8276-b5c3c30a2f32 Crash Report 2 - https://developer.apple.com/forums/content/attachment/b30a854d-3030-4227-a73a-f11b99ee69e9