Server Version#: 4.53.0 - Shield
Player Version#: 3.4.4
First of all, I like plexamp and mostly its worked pretty well for me, but lately if I press the play/pause toggle on my headphones, plexamp does not listen. The same is true for my Tasker scripts. They will play on plexamp, but not pause or stop playback. So, I"ve discarded permissions as a possible problem.
Regular plex player (same for podcasts) works with the headphone play/pause toggle, as does spotify.