This sounds as if some other process blocked the audio device when
switching back the session so that PA was unable to reopen the device
and thus playback stays suspended.
Could you please check this, by running "pactl" in a terminal when
this happens again, and then type "list-sinks"? If your sound card
sink remains in SUSPENDED state, than this is most likely the issue.
Or, you might have hit the well-known issue HAL where it fails to
restore ACLs sometimes and thus PA is not able to reopen the device
properly. Check getfacl /dev/snd/*
So, I'm intersted in this so I can try to debug this and provide useful
information for resolving this issue.
I tried running pactl, but get this:
[rodd localhost ~]$ pactl
No valid command specified.
I then tried
[rodd localhost ~]$ pactl list-sinks
No valid command specified.
Finally I did a check of man pactl and then tried 'pactl list' but this
gives a huge output, only some of which is 'sinks'.
How would I tell what state my sound card is in (currently it's working,
but I wanted to try all this while everything worked so I could see
what's changed.)