The company I work for has developed an app using Xamarin.Forms and while that process has had its ups and downs all of which I don't want to get into today, we pushed a version of the app to the iOS AppStore for TestFlight.
Apple came back to us saying it had been rejected due to a crash on load, so, we set off to investigate the problem
Steps we took
1. Build on an iPad using "release" as the configuration from within Visual Studio - App starts and runs as expected with cable still attched
2. Release an Enterprise build and download to the same iPad deleting previous "Release" build first - App crashes on load
3. Desymbolicate crash log
/Applications/Xcode.app/Contents/SharedFrameworks/DVTFoundation.framework/Versions/A/Resources/symbolicatecrash crash.crash OurAppIOS.app.dSYM >> desym.log
The result of this is the following
Incident Identifier: A6264392-5A4A-4BAE-AAA0-A93F0ACBEAA4 CrashReporter Key: 498211b599c1500911329b8b178711d115c06a7f Hardware Model: iPad6,7 Process: OurAppNew  Path: /private/var/containers/Bundle/Application/E8532546-68EC-48B5-AF53-1B719C1DB54B/OurAppNew.app/OurAppNew Identifier: com.company.OurAppNew Version: 322 (3.0.10) Code Type: ARM-64 (Native) Role: Foreground Parent Process: launchd  Coalition: com.company.OurAppNew  Date/Time: 2018-06-05 16:50:09.3275 +0100 Launch Time: 2018-06-05 16:50:09.2444 +0100 OS Version: iPhone OS 11.3.1 (15E302) Baseband Version: n/a Report Version: 104 Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x0000000000000000, 0x0000000000000000 Exception Note: EXC_CORPSE_NOTIFY Triggered by Thread: 0 Application Specific Information: abort() called Filtered syslog: None found Thread 0 name: tid_303 Dispatch queue: com.apple.main-thread Thread 0 Crashed: 0 libsystem_kernel.dylib 0x00000001822052ec __pthread_kill + 8 1 libsystem_pthread.dylib 0x00000001823a6288 pthread_kill$VARIANT$mp + 376 2 libsystem_c.dylib 0x0000000182173db0 __abort + 152 3 libsystem_c.dylib 0x0000000182173d18 __abort + 0 4 OurAppNew 0x0000000102a956ec print_callback(char const*, int) + 28956396 (runtime.m:1216) 5 OurAppNew 0x0000000102a83cec monoeg_g_log + 28884204 (goutput.c:125) 6 OurAppNew 0x000000010290d6f4 load_aot_module + 27350772 (aot-runtime.c:2099) 7 OurAppNew 0x0000000102966268 mono_assembly_load_from_predicate + 27714152 (assembly.c:2321) 8 OurAppNew 0x0000000102965dcc mono_assembly_open_predicate + 27712972 (assembly.c:1973) 9 OurAppNew 0x0000000102a94e28 xamarin_open_and_register + 28954152 (runtime.m:944) 10 OurAppNew 0x0000000100f55554 xamarin_register_assemblies_impl() + 382292 (main.m:109) 11 OurAppNew 0x0000000102a9c418 xamarin_main + 28984344 (monotouch-main.m:434) 12 OurAppNew 0x0000000100f556d0 main + 382672 (main.m:136) 13 libdyld.dylib 0x00000001820d5fc0 start + 4 Thread 1: 0 libsystem_pthread.dylib 0x00000001823a3b04 start_wqthread + 0 Thread 2: 0 libsystem_pthread.dylib 0x00000001823a3b04 start_wqthread + 0
This crash log is indicating that there's a problem within the Xamarin framework somewhere. We've ran the app a couple of times to get a few more logs and each of the logs come back to same.