Comment 21 for bug 1556439

Alsa is reporting that headphones are repeatedly plugged in and out, and that makes pulseaudio switch between headphones and spdif output. I'd guess that's a hardware defect. You can work around the problem by commenting out module-switch-on-port-available in /etc/pulse/default.pa. That will stop the output switching.

The crash seems to happen when a stream (in this case a bell sound from gnome shell) stops during an output switch. I don't know how that's possible, I'll continue investigation later.