I'm not sure what changed, but suddenly I can't get any sound through my headphone jack. When I plug it in, Ubuntu detects it. When I mute and unmute, I can hear the noise floor change. Pavucontrol shows a bouncing volume indicator, so it thinks it's outputting audio. The headphones work in other devices.
I've tried booting into an older kernel, force reloading alsa, reloading pulseaudio, and I've tried every proposed solution in this thread:
Nothing will get my headphone audio back. What should I do?