For what it’s worth, I’ve had this same issue: Chord symbol disaster after upgrading from 6 to 6.2.2 - #17 by jjm_335
I heard from Tim in tech support via email last week and, as far as I know, someone is investigating it — though it has been a while now. He sent me a link to revert to my previous version of Dorico (6.0) and my chords are working again. Would be nice to be able to update, though, and also to hear from someone from the development team via the thread above.