Man, I don't know what's going on anymore. I've tried to make it happen (opening loads of tabs in Chrome, running Resolve, Premiere, Photoshop, After Effects, MediaCoder, Avid all at once then quitting) again, but it's not playing ball.
I guess that's good?
All I've done is go back to 32bit Chrome, and uninstall a few redundant drivers (which was more general housekeeping than trying to fix this) - but surely if it was chrome then it'd show in Resource monitor as one of or the sum of the Chrome processes?
I'll post again when it happens.