Here is the solution to deal with the problem until Blizzard fixes it properly.
After applying update from xbox:
When changing games, shut down xbox, audio equipment and tv. Do not restart console, you have to do a cold start.
When you bring everything back up, everything will work. Changing games between Diablo IV and anything else may block out your sound again. If it does, do a cold start for all your equipment and you will be good to go.
Blizzard, get your sh*t together.