OK, as an update, I got it working, thanks to Oliver at MS Support.
It's an odd one, but essentially, these are the steps I took:
- Go to Device Manager
- Open up "Sound, Video and Game Controllers"
- Uninstall the "Realtek High Definition Audio (SST)" driver, BUT not remove the driver. Once done, DO NOT reboot yet.
- Go to Windows Update, and check for updates. Interestingly for me it found a "System Hardware Update for 11/2/2015".
- Now do an "Update and Shutdown".
- Oliver had me hold the Volume Up with the Power button. Not sure if that did anything though, since that just left me at the BIOS screen. Once in there, I just clicked on Restart, and booted up normal.
That's it... Once back in the headphone jack was working. Not sure what happened to cause the issue in the first place. Weird.
Hope that helps anyone else who runs into this odd issue.