Midi chain: OT out -> A4 in, A4 thru -> Tetra in, Midi Keyboard out -> OT in.
Channels: A4 auto channel 5, OT auto channel 6, Tetra channel 7.
No other midi channels set.
I select a midi track and set channel 7, Tetra plays all notes on both the OT keyboard and Midi keyboard as expected.
I select a midi track and set channel 6, A4 plays on both OT keyboard and Midi keyboard except notes C3, A3, and B3. They are dead silent.
HAELP
Note: The A4 plays all keys on the built in keyboard. The midi keyboard also plays all keys if i plug it directly to A4 in.
Solved: Another reboot and it started working >_<
Preserved for historical and humiliating reason