Yes I reported it to Steinberg 01/01/17 but as part of the general Mac OS sluggish GUI issue.
I have had a confirmation that my report was received but nothing further.
Thinking back my problems started when I installed Sierra. I was running Cubase 8.5 before it was deemed compatible by Steinberg and was expecting some kind of update but was surprised when Steinberg announced compatibility with no patch.
I bought the upgrade to Cubase 9 hoping it would fix it but it made no difference.
So I think Apple changed something in Sierra which affects how the mouse gets read by Cubase. So not necessarily a bug in Cubase as that didn’t change but rather a Sierra compatibility issue.
I also had the single click issue the others have mentioned - like the mouse is too sensitive to movement when clicking on an insert in the mixer - but this also went away when I removed the mouse pad.