Do you know what can cause this?
System sounds are working, I can play audio except in the browser which I just used with a JBL GO 2 to listen to a video. (Now, trying playing the same online content from another browser yields the same absurd result: perfect video, no sound. This time, neither a restart nor suspend and awake changed the error.) -- This particular instance was revealed as not a system error and an irrelevant nuisance; see my comment below.
HOWEVER,
the reason why I thought this to be a real issue was that similar phenomena occur frequently.
The bluetooth connection with the JBL device regularly (but inconsistently) malfunctions. The issues include an erratic pairing/unparing with that device without the opportunity for controlling, and a sudden cessation of the sound while playing video (occurring not so often as the former, but too frequently). The playback sound comes back after shutting down and reconnecting the bluetooth device; when even that leaves me without control of the bluetooth settings of the JBL, the computer must be suspended or restarted. Then, audio functions well again. (Other questions on askubuntu.com stated the same.)
Can you evade this recurring problem? (I have Ubuntu version 20.04.5.)