USB Midi has never worked properly with MPC X

2.1.1r installed but occurred in all previous firmware versions.

USB midi start/stop and clock seem to work fine but when sending a midi note from the MPC X, the Mono seems to force the MPC to latch each note. The note that is played on the pads is held on the MPC X and has to be tapped again to turn it off. I have never seen this behavior with any other device (Torso T1) or synth (Majella Implexus) that I have connected via USB. I have tried all MPC X and Mono midi settings but nothing has corrected the issue.

Also, when sustain is turned up on the Mono there is a constant note being played, like a drone, despite no note being played on the MPC X. This does not happen when the Mono is connected via DIN midi.

I have only ever had any success using DIN midi with my Mono. I have had this mk1 Mono for a few years now and have considered selling it so many times. It has never felt like it has worked properly.