I’m digging this thread up as I have the same issue, mostly with regular phone calls. The handsfree speaker output is way too loud and can’t be reduced (tried all available volume sliders in the settings), only by covering the speaker with my finger. Persists after reboots. I’m using bluetooth headsets regularly, maybe android gets confused by often switching between audio devices?
Here’s a similar thread, still sort of unresolved, too: Volume does not adjust during bluetooth phone call
Any experience or idea, anyone? thanks!