It happened to me twice.. One on the previous system version and one today after system update.
Just played with different ambiences and in one moment I noticed that phone without sounds. Can't play music, no notifications sounds etc.
Pressing on the volume buttons just show me "Muted"...
Tried to restart different processes like ambienced, lipstik etc, nothing help, but simple reboot restored all back.

Someone know which process exactly we can restart to get the sounds back without reboot ? I believe that should be simple solution for this..
Thanks