Welcome to the club ! Yes, it often sucks…
As to RME… Total Mix is a real beast, but once you know it it is an excellent tool and you can’t get around it, anyway. Not helping … I know …
But I have never had anything like that since TM exists nor where there any probs with RME drivers for roughly 12 years. Since there seem to be very few users with similar problems, it might be a system quirk at your side.
I suppose, you went through the usual fun part of re-installing RME & Nuendo drivers, as well as checking with the computers sound settings, already.
Good luck …
Big K