(N.B. subsequently edited to make corrections based on further tests)
OK there is something very weird going on here. Here, the “note choking” isn’t happening with external MIDI instruments, but it’s like there’s some kind of reset (other than CC123) being sent, because MIDI expanders that I’ve set up with sysex are going mute.
I havent’ gotten to the bottom of this yet, but what’s happening with one of my external MIDI instruments is, with playback running, I record-enable a track (it keeps playing) and everything is OK, but if I then stop playback and restart, the drum channel (on MIDI channel 10) is gone – this is a channel I set up with sysex at the start of playback. I have to go to zero and start playback again (which sends the sysex to the expander again).
I’ll keep investigating (while thinking, why should I have to do this debugging?).
[UPDATE:] just stopping and starting playback makes the external MIDI expanders reset. Nuts! (not true – corrected)
[UPDATE:] OK it was partly an issue with the MIDI part, which was imported from an SMF I was sent, so not so bad.
[UPDATE:] confirmed the issue described also happens with external MIDI, CC123 is being sent when the record-enable button is turned off.
In a MIDI sequencer, this is a show-stopper bug. 