I did more troubleshooting with the user having the issue. Originally the user was using a Poly BT600 Headset. When I had the user switch to phone audio the mute/unmute functioned as normal.
I also had the user switch to the internal microphone and the mute/unmute functioned as normal.
I finally switched back to the BT600 Headset and the functionality broke again. I had the user power off the headset and remove the wireless dongle for about a minute and then reconnect to no avail.
Suspecting that it has more to do with the Poly BT600. I will circle back and make sure the headset is on the proper firmware and do more testing.