CC121 fader has a life on it's own in C7.5 (flawless in C5)?

Since I updated from Cubase 5 to Cubase 7.5 - a couple of weeks ago -, my Steinberg CC121 controller has been acting incredibly frustrating lately.
My MR816 interface has some problems with Cubase 7.5 as well (LOTS of - CPU related? - audio drop outs, where the only real solution is switching to another sample rate, and back. But that’s a problem for another time and topic).

About 50% of the time, when I touch, push or ‘hit’ the fader, the fader shakes a little and drop down to zero. Cubase doesn’t register this, unless I try to turn the fader back up. The only solution is switching to another channel, and back.
Restarting Cubase doesn’t fix the problem. Restarting the whole system however, does.

Cubase 7.5 and CC121 both have the last updates. All help is more than welcome!
Is Steinberg/steinberg users familiar with this problem?

Best regards,