My experience too - at least for one of my projects - only seemed to happen on the first playback on .20 though but no sure.
This behavior has been the norm for me since Cubase 7. Typically, I let the Project run through once to let it glitch at various points where different Instrument track parts show up along the timeline…then the next playback is good to go. But not with 9.0.20. The glitches continue until I raise the buffer to what I consider an unusable amount for recording. Rolling back to 9.0.10 fixed the problem for me.
Has anyone noticed that Steinberg has left the the 9.0.10 update link at the top of the forum page? Usually, they remove the previous version from up there. I think they are aware that 9.0.20 is problematic for some (or many) users and left the 9.0.10 link as a safety measure.