The midi hangs is always difficult to catch. Specially with midi over USB.
More common reason is that the CPU is doing something else while it receives to many midi infos and misses NOTE_OFF.
I'll give a try playing chords while changing the algos with midi over USB.
In the meantime, when that happens, you can push "+" and "-" at the same time to stop all notes. No need t
You can also try to set in MENU>Config>Send to "No" if you don't need it.