Same problem here on Debian unstable with LXDE. It seems timidity is
claiming the sound device before PulseAudio can.
# fuser -v /dev/snd/*
USER PID ACCESS COMMAND
/dev/snd/controlC0: timidity 635 F.... timidity
/dev/snd/pcmC0D0p: timidity 635 F...m timidity
/dev/snd/seq: timidity 635 F.... timidity
/dev/snd/timer: timidity 635 f.... timidity
# systemctl stop timidity
# fuser -v /dev/snd/*
#
After logging in again as a regular user, pulseaudio daemon starts
again and now is able to claim the sound device. Now sound works again.
HTH,
Peter Nowee
