Unreal ignores all unused signals in FUnixPlatformMisc::SetCrashHandler which messes with the mono signal setup such as this. Ignoring unused signals seems unnecessary as handlers wont get called unless explicitly hooked up? There is a workaround for mono sub-processes but this doesn't help with embedding mono. Perhaps @RCL might know the reasoning for ignoring signals and a possible workaround?

C# threads crash when they exit. There can be various errors but the most common is an assert on mono_bitset_test_fast. The only info I have found on this is an issue in libTAS which mentions something about thread recycling. This threading issue doesn't happen on Mac or Windows.