OK, so I was wrong about seccomp. That’s progress at least 
You might be able to get some hints by running the app through strace, but that is in-depth and difficult to read the output, and may not be helpful anyway. It still a good thing to try, though. Using strace might, for example, allow you to correlate that a particular syscall returned a result the app didn’t expect, such as being unable to find a particular library.