Get MIDI Wrench app (its free) to see what’s going on.
I had a similar problem OT MKII not sending correct midi channel or cc messages
The note off info wasn’t being sent on the correct channel, leading to hung notes.
It’s deffo something about the octatrack as my midi thing worked fine with all my other gear. The fix was to get a better usb to midi thing, I got a roland um-one. Maybe visit a music store and see if they have one you can test.