App is crashing on startup in Apple App review, but I cannot replicate it

Question

Created Mar ’23

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Can anyone help me with this crash? It crashes on start up according to the App Review. It was written in C# using Xamarin iOS. I've tested the app in debug, release, and TestFlight on both iPad and iPhone and haven't been able to replicate the crash.

Here's part of the crashlog, I couldn't fit the whole thing in the question. If you need anymore information let me know.

Incident Identifier: 432AD166-AABB-4FC4-AF07-4EBDFEE80E9D
CrashReporter Key:   7f13e1dee0a0434b3c240288b1caae098e3628f0
Hardware Model:      iPad11,3
Process:             App.iOS [22414]
Path:                &#x2F;private&#x2F;var&#x2F;containers&#x2F;Bundle&#x2F;Application&#x2F;16369005-2E1C-4457-A763-5E8AAECBAE73&#x2F;App.iOS.app&#x2F;App.iOS
Identifier:          com.Name.App
Version:             1.5.2 (1.5.2)
AppStoreTools:       14C17
Code Type:           ARM-64 (Native)
Role:                Foreground
Parent Process:      launchd [1]
Coalition:           com.Name.App [7168]

Date&#x2F;Time:           2023-03-21 14:26:38.9981 -0700
Launch Time:         2023-03-21 14:26:33.2442 -0700
OS Version:          iPhone OS 16.3.1 (20D67)
Release Type:        User
Report Version:      104

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Triggered by Thread:  22

Application Specific Information:
abort() called

Thread 22 name:  Thread Pool Worker
Thread 22 Crashed:
0   libsystem_kernel.dylib        	       0x1dbc79674 __pthread_kill + 8
1   libsystem_pthread.dylib       	       0x1ec31b1ac pthread_kill + 268
2   libsystem_c.dylib             	       0x1a60e43e4 __abort + 128
3   libsystem_c.dylib             	       0x1a608cc98 abort + 192
4   App.iOS               	       0x108725b04 xamarin_find_protocol_wrapper_type + 92805892 (runtime.m:1189)
5   App.iOS               	       0x1085ec414 mono_invoke_unhandled_exception_hook + 91522068 (exception.c:1299)
6   App.iOS               	       0x10869a45c mono_thread_internal_unhandled_exception + 92234844 (threads.c:6010)
7   App.iOS               	       0x108691ad4 worker_callback + 92199636 (threadpool.c:0)
8   App.iOS               	       0x10868f2e0 worker_thread + 92189408 (threadpool-worker-default.c:502)
9   App.iOS               	       0x10869aa74 start_wrapper_internal + 92236404 (threads.c:1289)
10  App.iOS               	       0x10869a8f8 start_wrapper + 92236024 (threads.c:1310)
11  libsystem_pthread.dylib       	       0x1ec3156cc _pthread_start + 148
12  libsystem_pthread.dylib       	       0x1ec314ba4 thread_start + 8

Thread 22 crashed with ARM Thread State (64-bit):
    x0: 0x0000000000000000   x1: 0x0000000000000000   x2: 0x0000000000000000   x3: 0x0000000000000000
    x4: 0x0000000000000000   x5: 0x0000000000989680   x6: 0x0000000000001200   x7: 0xffffffff00000c00
    x8: 0x2dc423abece235b1   x9: 0x2dc423aa82b745b1  x10: 0x00000000000003e8  x11: 0x0000000000000000
   x12: 0x000000011af47800  x13: 0x000000010c3aaf13  x14: 0x00000000000000e0  x15: 0x0000000080000000
   x16: 0x0000000000000148  x17: 0x000000016e557000  x18: 0x0000000000000000  x19: 0x0000000000000006
   x20: 0x0000000000009103  x21: 0x000000016e5570e0  x22: 0x0000000000000082  x23: 0x0000000281a63d80
   x24: 0x0000000124a6c400  x25: 0x000000010c3ac778  x26: 0x0000000108f36000  x27: 0x0000000108f364e0
   x28: 0x0000000108f36538   fp: 0x000000016e556bd0   lr: 0x00000001ec31b1ac
    sp: 0x000000016e556bb0   pc: 0x00000001dbc79674 cpsr: 0x40000000
   far: 0x0000000119779008  esr: 0x56000080  Address size fault

Binary Images:
       0x1dbc72000 -        0x1dbca9feb libsystem_kernel.dylib arm64e  &lt;c76e6bed463530c68f19fb829bbe1ae1> &#x2F;usr&#x2F;lib&#x2F;system&#x2F;libsystem_kernel.dylib
       0x19ea08000 -        0x19ededfff CoreFoundation arm64e  &lt;42ccfc7bff323d258f01ccb2ad843a8b> &#x2F;System&#x2F;Library&#x2F;Frameworks&#x2F;CoreFoundation.framework&#x2F;CoreFoundation
       0x1d83cf000 -        0x1d83d7fff GraphicsServices arm64e  &lt;85419099269b336d86b40d52d0ff6923> &#x2F;System&#x2F;Library&#x2F;PrivateFrameworks&#x2F;GraphicsServices.framework&#x2F;GraphicsServices
       0x1a0bdd000 -        0x1a23d0fff UIKitCore arm64e  &lt;cf21ad9cefbf3961a7c054bd30cefea9> &#x2F;System&#x2F;Library&#x2F;PrivateFrameworks&#x2F;UIKitCore.framework&#x2F;UIKitCore
       0x102ea4000 -        0x1089cffff App.iOS arm64  &lt;4d7629105d1b35a990677a0d08acf170> &#x2F;private&#x2F;var&#x2F;containers&#x2F;Bundle&#x2F;Application&#x2F;16369005-2E1C-4457-A763-5E8AAECBAE73&#x2F;App.iOS.app&#x2F;App.iOS
       0x1bd35f000 -        0x1bd3e2093 dyld arm64e  &lt;4b042f280d1430eca1de3dbb10866ad7> &#x2F;usr&#x2F;lib&#x2F;dyld
       0x109d74000 -        0x109ebbfff grpc arm64  &lt;fecc71db1ff036b1bf861008c6743cdf> &#x2F;private&#x2F;var&#x2F;containers&#x2F;Bundle&#x2F;Application&#x2F;16369005-2E1C-4457-A763-5E8AAECBAE73&#x2F;App.iOS.app&#x2F;Frameworks&#x2F;grpc.framework&#x2F;grpc
       0x10a10c000 -        0x10a147fff grpcpp arm64  &lt;92766c3033453065a14896c21ec7080c> &#x2F;private&#x2F;var&#x2F;containers&#x2F;Bundle&#x2F;Application&#x2F;16369005-2E1C-4457-A763-5E8AAECBAE73&#x2F;App.iOS.app&#x2F;Frameworks&#x2F;grpcpp.framework&#x2F;grpcpp
       0x1a6025000 -        0x1a606bfff libdispatch.dylib arm64e  &lt;ded4d0a5142032ae83a6c31d938a1c9a> &#x2F;usr&#x2F;lib&#x2F;system&#x2F;libdispatch.dylib
       0x1ec314000 -        0x1ec31ffff libsystem_pthread.dylib arm64e  &lt;45ac734e66493ee2a0963fd66441ab78> &#x2F;usr&#x2F;lib&#x2F;system&#x2F;libsystem_pthread.dylib
       0x19fb9c000 -        0x19ff65fff CFNetwork arm64e  &lt;7f3313c9143533338c82dc961429d0b3> &#x2F;System&#x2F;Library&#x2F;Frameworks&#x2F;CFNetwork.framework&#x2F;CFNetwork
       0x198dee000 -        0x199737fff Foundation arm64e  &lt;e5f615c7cc5e3656860041c767812a35> &#x2F;System&#x2F;Library&#x2F;Frameworks&#x2F;Foundation.framework&#x2F;Foundation
       0x1a606c000 -        0x1a60ebff7 libsystem_c.dylib arm64e  &lt;3cd8c9e025fd3b29850774cdffe7f16c> &#x2F;usr&#x2F;lib&#x2F;system&#x2F;libsystem_c.dylib

EOF

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Answer 1

iAmBowser OP

Mar ’23

Based on the crash log, it seems that the crash is happening on a background thread (Thread 22), but it's difficult to identify the exact cause without more information. Here are some suggestions to help you troubleshoot the issue:

Symbolicate the crash log: Symbolicating the crash log will provide more human-readable information, such as method names and line numbers, which will help you pinpoint the problematic code in your app. You can use Xcode's atos tool or symbolicate the crash log within Xcode itself. Here's a guide on how to symbolicate crash logs: https://developer.apple.com/documentation/xcode/analyzing-crash-reports

Inspect your multithreading code: Since the crash is happening in a background thread, carefully review any code that spawns new threads or manages concurrency, such as DispatchQueue, OperationQueue, or any Xamarin-specific libraries you are using. Ensure that you are using thread-safe data structures and that you're not accidentally accessing UI elements from a background thread.

Test on multiple devices and iOS versions: As you mentioned that the crash occurs on startup according to the App Review but not on the devices you tested, try testing your app on various devices and iOS versions. You can use the iOS Simulator to test different device models and iOS versions. This might help reproduce the issue and narrow down the cause.

Check for memory issues: Ensure that your app is handling memory correctly, especially in multi-threaded scenarios. Look for memory leaks, over-releases, or other memory-related issues that could lead to a crash. You can use Xcode's memory debugging tools (e.g., Instruments) to help you find and fix memory issues.

Enable exception breakpoints: Enable exception breakpoints in your debugger to help identify where the crash is occurring. This will pause the debugger when an exception is thrown, allowing you to inspect the call stack and local variables for more information about the crash.

If you're still unable to identify the issue, consider sharing the symbolicated crash log and relevant parts of your codebase (especially those related to multithreading) so that others can help you troubleshoot the problem more effectively.

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