I started experiencing this in Nuendo 8.5 I thought it might be graphics drivers, but 6 months of graphic driver updates hasn’t solved this. Finally upgraded skipping Nuendo 9 to Nuendo 10 and was surprised to see this still here - so reporting it now.
I am not sure how it gets to this point, but it doesn’t happen right away - perhaps 30-60 minutes of editing and then I started noticing it.
PC Windows 10 64bit - latest graphics drivers, GTX1070ti
Nuendo 10.2 B284
ADD: I literally updated my graphics driver again after this post. The issue seemed to be gone - then about an hour or two into the session it started happening again. So I am now thinking that there is a memory leak or resources aren’t cleaned up properly.