Mid timing is inconsistent full stop. NOTHING to do with Cubase.
I’m afraid this is going up it’s own RRRRRRRs. 
I’ve explained the problem to you. Get over it. Move on.
And don’t forget to ask for a bunch of jitters next time you’re at the grocers.
BUMP ! 
Just discovered this since starting to use external synths/mixers and bouncing alot of audio in cubase (before that it was just offlining a laden project … Not so say I didnt have those problems in offline - but definitely have em in realtime bouncing of external synths.
It was also more noticeable to me at high bpm projects.
I currently am getting drifts of 3 and 6 samples @145 BPM, 48K (cubase 5.52, winXP)
My cubase is not synced to my (Sonic Core) card. I am currently studying the problem and will try external sync (never used it)
Any updated conclusions on the matter ?
I also noticed that when rendering midi Instrument to audio , you can early see the timings slightly different on every hit