Cubase vst instruments playback problem

Hi everyone,
I recently updated to C10 pro from C6. Everything seems fine except for this one odd problem. All stock Cubase pro 10 vst instruments only play on the left or right channel- not in stereo. Other vendors’ vst instruments play normally in stereo.
When first loaded they play OK for a few seconds then shift either left or right. Any ideas how I could fix it?
I’m on Win 10 running the latest C10 pro version.
Has anyone come across this issue? Is it a known bug I know nothing about?
Thanks in advance,
Kris :bulb:

No, that’s not normal behavior at all.

No real good ideas about the cause, but maybe:
Check if there is any accidental panning automation.
Are they somehow being created on mono tracks (is that even possible?)

You could try trashing you Preferences so they get rebuilt.

Thanks for your reply. I have already trashed preferences, reinstalled C10 and also installed C9.5. Same problem in 9.5.
I’ve never had such a problem with C6. The ‘funny’ thing is it only affects steinberg vsti’s. This basically renders Groove Agent SE unusable since it only plays on 1 channel. I don’t really use steinberg vsti’s except for GA so it’s a major pita for me.
Looking forward to more ideas.