wow…haven’t heard that in a long time. I had that happen in an earlier version of Cubase. In my case, it turned out that I did something (sorry, don’t remember the full details becauses it was around 10 yrs ago)…and I was using other outboard gear/SMPTE via midi etc…and it was that something was switching things to fulfill it’s own needs, leaving my midi interface (LynxOne) in a state that did some fuunkkay…things to my cubase assignations.
Dunno if that helps, but it sucks to get left hangin’ here…
Hope you figure it out
Cheers