Alert volume (not system) consistently reset to zero for unknown reason Several times a week I find that, despite my volume being set to a reasonable setting, I receive no alert sounds (slack, messages, etc). Every time, the alert volume is set to 0. See picture below. When I see this, I crank up the alert volume and all is well.
My best guess at the moment is this has something to with hooking up my laptop to my work desk. I use it in clamshell mode, so I hook up the display port cable and my headphones, etc before the machine is fully awake.
Has anyone else run into this problem? Any thoughts on what I should be looking for?
Try completing an NVRAM / PRAM reset. This is the part of the computer that often holds these values in memory and can sometimes become the source of this type of issue....


Reboot your computer.
Hold Command + Alt + P + R
Wait until you hear the startup sound/chime a second time, during this time the computer will reboot.


If the computer does not chime a second time but instead boots up you've not pressed the shortcut quickly enough, you can press it as soon as you've pressed reboot, and sometimes need to use a wired not wireless keyboard for this.

Verify of the issue is resolved.

Further details on Apple's website