I've had that same problem from day one, with the stock rom, S8LightRom and now CleanRom. The back and menu buttons are both pretty much useless because they refuse to be pushed only once. I thought for sure I had a broken one, so seeing all of the others here with the same problem is actually kind of a relief in a sense.
As a side note, I also had the NVRAM 0X10 error for weeks after upgrading to CleanRom and finally just got that cleared up today. If someone could fix the back/menu buttons problem (and maybe somehow bring back the compatibility with the Magisk module to increase the number of steps on the volume sliders, for some reason that disappeared when I upgraded to CleanRom) it'll all be golden.
Just thought I'd chime in to help legitimize the problem, thanks so much to everyone here for all of the help and info thus far.
All the best.