Hardware/firmware problems are incredibly difficult to diagnose - and convincing the manufacturers that they have a problem is even more difficult.
I once spent several months, culminating with a week flying around the American Midwest, because of this sort of thing. My contribution was to spend 20 minutes showing the user how to replicate the problem without using our software at all. The user was a very nice guy who had something like $500,000 of kit and wasn’t paying until it was working to his satisfaction.
I got a pleasant stay with our local rep and Saturday in Washington and a chance to visit the Air and Space Museum.