I have a VIM3 with the most current android version and a tone board.
Until today it worked flawlessly until it suddenly turned the volume down.
Making it louder in the settings wouldn’t work.
If I plug the toneboard in my pc, everything works fine again.
You said that everything works well with the PC, while there is a problem with the vim board, so I think that somewhere there is a bad contact in the TB + vim bundle
I have checked for that first.
Even if there was a weak contact I cant understand why that would make the volume lower and not just output nothing at all.
Please note also, that moving the volume bar in android over step three does not change the volume, only changing it under Step 3 changes the volume.
in vain you think so, just the board can behave differently, it is not necessary that it will not work for you at all, the very concept of “bad contact” or “no contact at all”, these are different things.
Try turning on the sound and shaking the board a little (not much).
as @Vladimir.v.v recommended, did you try backing up and reflashing Android to see if that works ? because it could also be some stubborn byte that is refusing to change the volume…