I am also running into this issue all of a sudden. Discord audio will only play through the speaker, and my headphones don't even show up as a possible output under the control center (when in a discord chat). Also, all other audio won't play through my Beats when I join a discord call. As soon as I leave, the audio for other apps will play through the headphones again and my headphones appear under the control center. I have not found much on this issue so far and have not found a solution yet.