This seems to be a problem with any generic remote. I attempted to assign control room volume to a simple fader on one of my midi controllers (as the Eucon control room knob is too inaccurate), but Cubase keeps forgetting the assignment.
I even tried adding a new mapping (vs. the default VST1-8, etc), but that is lost as well. Renaming a default mapping doesn’t even work after a restart. All is fine until Cubase is restarted, then it’s gone. Have to remap it manually everytime - how in the heck can Steinberg screw up something like this that worked for years?