The same thing happens for me. I'm a person who chooses by image, so I'm in great trouble.
Have you tried increasing the volume of the game in the settings?
It doesn't go down on its own, but it's worth checking out.
If it doesn't go down ... I'm sorry,I don't know.
The same thing happens with my Nintendo Switch.
However, this could be a bug in Minecraft, but I think it could also be a bug in your Microsoft account.
But now (albeit a bit annoying) you'll have to log in every time, or play without logging in until it's improved.
It didn't happen on my switch.
I would appreciate it if you could tell me the situation when it happened.