Date: June 12ish-13ish, 2018 update.
Suspected Cause: Kernel update from 4.13.0-43 to 4.13.0-45
Have a Thinkpad T420 and just updated today. Tried watching a Youtube video and noticed my dedicated volume buttons no longer work and I had no sound. Same goes for mute speakers button and mute mic button. I can get audio to output but I have to go up and toggle on the on/off rocker and manually adjust volume from top menu bar, but only system sounds are heard nothing from the browser. What is even stranger is that when I go into sound settings it shows no output or input devices! Any advice?