Pulsesink stopped working (Linux)

I’ve got Mopidy running on Ubuntu - all lovely running as a service using the Pulseaudio config instructions here. For weeks it was fine playing music alongside Firefox, etc - i.e. the audio was correctly routed through pulseaudio. It’s now not working - and I can’t work out why!

I try to play something (using ncmcpp or mobile) and, although the track appears in the playlist and the frontend says “playing”, no sound comes from it and the time position in ncmcpp never moves from 0:00.

If I deactivate the pulseaudio config, I can get music to play from mopidy, but then that prevents all other sound.

Here’s my modify config

Here’s my mopidy.log

I additionally tried using paprefs as described here (and restarting both mopidy and pulse), no change.

Anyone else seen this behaviour recently? Any clues on how to diagnose? I’d be happier if I could spot an error message of some sort…!