Weirdly, I'm getting this on 2020.12.0.
Today I couldn't take it anymore, so upgraded to the latest and still have this issue.
I'm taping a sign on my screen's bezel: "Don't move clip gain during playback!"
This is also from a session with imported AAF tracks for dialog, so they may have some corruption of some sort in them, who knows!?!
I'm thinking the video editor (who's still a bit new to Resolve), may have spit out a strange version of an AAF maybe.
Anyway, this is just for update's sake, for anyone else encountering this bug (caused by external file issues, likely).