Hello,
There is an editor here who has had an issue where his menu’s will only show up when the hot key is used. Navigating through the menus and clicking on devices and any option inside that menu doesn’t yield any results. We have trashed the preferences and reinstalled and I even blacklisted some plugins he had added.
Anyone else seen this behaviour in N6.0.7?
This problem is related. Added a Eucon device and everything went back to normal.
That one had me scratching my head for a while.
There are definitely problems with 10.9x and Nuendo graphics-- and Steinberg knows about it.
What’s interesting to me in your case is that adding a Euphonix device fixes things for you.
For me, that’s part of what appears to break it!
I’ve learned to deal by clicking on Nuendo’s icon in the dock after starting up, before starting work. Normal behavior follows.
Tech support says this issue isn’t going to be fixed this time around (at least that was what I was told before Yosemite was released). Maybe it’ll be taken care of when the Yosemite-ready revision comes out. Maybe? 
Chewy