That’s strange. What are the values of Setting->Sounds & Reaction?
Looks normal to me, “do not disturb” is not activated, but I can’t tell how it looked when the bug happened (I had to restart the device in order to bring it back to normal working order).
Is an ambiance set with no sound? If yes, see this bug.
I haven’t swiched ambience since many weeks, thus I don’t think this bug applies here.