Thanks for the bug report.
From what I can tell, it looks like the stack trace points at a crash from the message being passed to Unity / MonoVM from the message processing thread rather than the Unity main thread where it's supposed to occur. In particular, the bold part of the callstack should not be happening:
#00 pc 00000000005b8dec /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/libunity.so
#01 pc 00000000005cc0ac /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/libunity.so
#02 pc 0000000000128b0c /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/libmono.so
#03 pc 0000000000022564 /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/libmono.so
#04 pc 00000000002c1b21 /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/libmono.so
#05 pc 0000000000018968 /system/lib/libc.so
#06 pc 00000000000d6a0e /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/
libFirebaseCppApp-5.2.1.so (firebase::messaging::ProcessMessages()+1609)
#07 pc 00000000000d71b5 /data/app/net.company.our_game_id-C_1SEdVsu0hPbyZjbqM8sw==/lib/arm/
libFirebaseCppApp-5.2.1.so (firebase::messaging::MessageProcessingThread(void*)+124)
#08 pc 00000000000478d7 /system/lib/libc.so (__pthread_start(void*)+22)
#09 pc 000000000001b341 /system/lib/libc.so (__start_thread+32)