doesn’t sound healthy, sounds like you tried all the right stuff, contact support for advice, if you reloaded os, then it’s not anything user related, assuming you have no midi devices hooked up, but doesn’t sound plausible, good luck with it
There is a chance that it may be that there is a software problem, but I’ve had a panning issue on audio in and others.
I’m sure you’ve tried this, but maybe there is a performance setting to pan on track 3?
Anyway, good luck with it, get the issue raised with Customer Support if no joy.
It does seem strange, because if it is a hardware problem, I would imagine there would be distortion, crackle, intermittent problems (not that I know anything about electronics, but from my experience with electrical audio devices).