Hello thanks for looking at this.
Its any software.. I'm analysing with Snoize Midi Monitor currently. I use Logic and Pro Tools.
I have tried..
Mac OS Sierra 12.5
Mac OS High Sierra 13.1
I have tried removing RAM sticks. Reseating the card in a different slot.
What happens is that the midi behaves completely normally, and then after a few minutes, generally after a period of inactivity (but not always) what should be note data says "Stop" or "Reset" or "Clock" command.
I have changed all cables.
I have changed the source to a different keyboard.
I am now about to try a different manufacturers USB midi interface to see what happens there, but first impressions are that this one still works whilst the RME doesn't.
Midi OUT seems unaffected.