Headphone jack stopped working

My headphone jack has inexplicably stopped working.

The speakers work fine and the Sound settings dialog recognizes when headphones are inserted or removed but the sound does not come out.

I do hear a brief connect / disconnect arc in the headset as the plug goes in and out but no computer audio.

I have tried different headphones both traditional 3-pin and 4-pin ones with microphones and no sound.

I have been living with this problem by plugging my headphones into my external monitor and selecting that output.

I have just tested the headphone jack using a Linux Mint Live USB stick and it works fine. My headphones continue to not work in PureOS after rebooting.