It could be a few things, as suggested by the rest of users in this thread, check all the Menu settings and MIDI page settings before anything.

If you want to make 100% sure, you can use some MIDI monitoring Software like MIDI-OX, that will tell you exactly what MIDI is coming from the OT if any.

There is deffinitely something going on with the OT and MIDI. A while ago I couldnt get any notes OUT to my Virus TI using the Arpeggiator, just turning Sync Clock Out to Off would fix it, somehow the project was corrupted and nothing got fixed untill I rebooted the unit and created a new project.

I was just working yesterday in a quick demo, to make a youtube video using the Quneo MIDI controller to trigger slices and scenes on the OT externally, and ran in to a few funny problems-bugs.

While working normally with audio tracks, I decided to make a MIDI track and use a x0xb0x for the bassline. In the Mixer section, the mutes of the MIDI tracks were all lighted up, half green half yellow… weird…

I couldnt trigger the x0xb0x at all, was going crazy, then decided to forget about MIDI track 1 and use MIDI track 2… Things started to work, but same weird Mute behaviour, even with all the MIDI mutes Off, now the x0xb0x wouldn´t shut up…

I then decided to turn it off, make an OS upgrade to the same one, and create a new project… things started to work normally again…

It might be some stuff going on that fucks up MIDI side of things.
Hope it helps!