I have been using Studio One for about four years now. I don't think I've ever had the issue I'm about to describe.

I have about five or six MIDI tracks, most of which use my Yamaha MOXF6 synthesizer. From time to time, as I work on a song, I set the voice number on my synthesizer to the intended voice for a specific MIDI track, and record the playback of that single MIDI track to an audio track.

The song I'm currently constructing started out without any issues. However, a couple days ago, I recorded a few measures in front of existing MIDI content for my organ track. Now when I play that track, it'll playback fine one time only. When I try to play that MIDI track again in the same Studio One session, the program will signal that MIDI messages are being sent, but I don't hear anything at all from my synthesizer. I can try it over and over, and it doesn't change. It's not until I close the program that I suddenly get a whole barrage of MIDI notes suddenly blasting into my ears from my synthesizer. So it's like these messages are being queued up, but aren't actually getting sent or received until I close out Studio One.

One top of this, yesterday, I recorded some MIDI notes to the end of a different MIDI track for bass, and now the exact same problem exists for that track. It'll playback one time just fine in a given Studio One session, and then it won't play anything afterward.

Although only those two tracks trigger the problem, the problem prevents *all* MIDI messages from playing the instrument, regardless of the track.

Has anyone ever experienced this issue? It's very odd to me, and it's making my song increasingly difficult to work on. Please help!

Specs:
Studio One Professional 5.5.2
Windows 11
16 GB RAM
256 GB SSD (where Studio One is installed)
1 TB SSD (where all project data resides)

Relevant Equipment:
iConnectivity MioXL (send/receive all MIDI messages to/from all instruments)
Yamaha MOXF6 (connected via DIN cables)