First, check that you've got the sound turned on in our mobile app.
Account → Settings → Sound
Turn on the sound option if it's not activated. This should return the sound to normal while playing a game.
Restart your mobile device if the issue continues.
If the sound is still a problem:
If you still have issues, let us know:
Also, send us the log files from our app:
Account icon → Help → Send Log Files to Support → SEND LOG FILES
Important:
Send us these files as soon as you can, as they will be overwritten after 48 hours.