Hi IOhannes,
thank you for good troubleshooting suggestions, albeit with no obvious solution:
->When putting a stderr output message at the start of that function followed by a sleep(10) command, the message appears but error occurs ~10+ seconds later, so happened after that code -> When putting a stderr message at the end of that function followed by a sleep(10) command, the message appears and the error appears, everything else (like both midi notifications) happens later, so the error appears to be triggered earlier than the sleep() command but took a while to produce a message. Actually it looks like it happened around that fork() call in this function. So a race condition may be possible between the parent and child of the fork (or it took a while for one or the other to die from different reasons...).
I'm keeping digging but am hoping there's some configuration details that I missed.
Cheers, Wolfgang