Correction of previous message:
The dropouts kept coming despite all taken ‘measures’. (grrrrrrr…^&(^@%^@) 
They occurred a couple of times during recordings and it turned out that Cubase itself ran out of sync after dropouts.
At the end I decided to try a UR824 (USB2.0) and purchased one. (because of integration in Cubase = 100%)
Wow this is a great step forward in speed (reactions) and stability (rock solid), not one single problem/glitch in one week of many hours using it. Even my CC121 works smoother now. 
I wish I knew this earlier : USB2.0 works much better than FW.
My MR816CSX ? For Sale!