Okay, checking out your screenshots… I don’t see any red flags so far. I can’t speak for the quality of UA drivers on Mac… I’m using RME. I wonder if there’s a driver issue? Unlikely, but possible.
Only thing that pops out at me, now that I think of it, is VSTBridgeApp… if you’re running 32-bit plugins in VSTBridge for Cubase 64-bit… that might be causing some of your headaches. I’ve completely moved away from 32-bit plugins due to poor performance of VSTBridge.
So… perhaps there’s some slight issue wth VSTBridge and/or the UA driver?
So, perhaps a test by removing any 32-bit plugins from your session.
OR, try running Cubase in 32-bit mode and see what happens… the way you do that is by going to Applications folder and right-clicking on Cubase, then click on Get Info, then click on Open in 32-bit mode.
Other than that, I suspect there may be some sneaky issue with a plugin and 10.9.2 – some plugin I haven’t tested…
FYI - I just loaded up a test session with 48 VSTi tracks all playing simultaneously with high total polyphony, and with 144 VST plugins on top of those tracks, using Cubase 7.5.10 on OSX 10.9.2 at 256 sample latency on an RME device – it was totally stable, nothing strange so far. So for me, I feel pretty confident with 10.9.2.
Will report back if I spot a problem that might be related to 10.9.2 on my system, but I doubt it at this point.
Anyway, I hope you can work out your situation and get it running smoothly!
Please post with your status either way, would be good to know what you find out…