MIDI connection restarting does not re-enable MIDI output to device if USB connection reset.
If the MIDI keyboard USB connection is lost, when restarting MIDI subsystem, output to device under I/O on preferences does not work. Workaround: Keyboard must be connected at program startup. If USB connection is lost, MuseScore must be restarted to re-enable output to keyboard.
It works just fine if using a plain MIDI controller for input only. (Tested with M-Audio Keystation 49es) Just as likely that it is on the Windows side of things and probably should just be something to update in the instructions. Definitely not a deal breaker.
Suggested text: If using MIDI output to device for program output, device must be connected at MuseScore startup. Restarting MIDI sub-system is not sufficient on all USB MIDI connections. If USB connection is reset, restarting MuseScore will re-enable output to device.
MuseScore OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 188.8.131.5288, revision: 148e43f
Keyboard : Roland FP-30