I just had the same thing happen the other day when I took it out of the case after charging it. The right Surface earbud has mysteriously stopped playing music or podcast or any sounds. The earbud is still connected. The gestures still work. When I take it out of my ear, it will turn off the music in the other ear.
I tried removing and readding it to my phone (Samsung). No luck.
I tried resetting to factory settings. No luck.
I tried reconnecting them to my laptop (Surface). No luck.
Tried reinstalling the Surface audio apps. No luck.
Tried cleaning them. No luck.
Tried meditating. No luck.
Am out of option. Am really worried to be out $200! If so, not going to trust my Microsoft device purchases.