FWIW

I really haven't been playing with iRP as much lately, and when I have, I've been mostly using the internal speakers of my iMac and did not notice the dropouts happening.
I've only had one quick instance when the problem happened again, and I was using my Babyface (original) audio interface at the time.

I suspect that the drivers that RME supplies for this discontinued product might not be up to snuff with the current versions of MacOS, although their download site says they still are.

I'd try running the Babyface in Class Compliant Mode, which bypasses RME's drivers, to see if that helps.
But then the only way I can control the BF's volume is at the interface itself (i.e. no software mixer) which is not practical with my current setup.

I've tried everything else suggested in this thread so far.

Is anybody else out there using an original (i.e. non "Pro") version of the Babyface w/o this issue?
I suspect that this problem is driver oriented.