We found this issue at Rizumu Nightclub ( https://vrchat.com/home/world/wrld_912760ee-aa19-4442-8b6a-b81721aeb8f0 )
There will be 30+ people in an instance, and I found two people whose audio were 10x louder than everyone else (ignoring the override zones).
Having them rejoin the world instance fixed their audio levels.
I do not know steps to reproduce. It may be random, or not...it's a nightclub world: many users were in the world instance for a few hours. 95% of people applied overrides correctly.
I'll leave this here as another strange experience I had but unconfirmed (please chime in if you've seen this): In the Great Pug, I met a user whose nameplate showed he was talking but couldn't hear him (like the zone in the back of the kitchen). He was fixed after rejoining.