MIDI export of a part crashes
In libmscore/rendermidi.cpp at the place where
events->registerChannel(channel) is called,
-1. This leads to a crash later when that is reinterpreted as 255 (uchar).
In 2.x the channel was set to the correct value here. In master, it’s only correctly set for the, no pun intended, master score, not for the parts/excerpts.