Error: Couldn't Retrieve the Play Queue for This Item on Apple TV



My Plex server running off a Synology NAS has been running flawlessly for the past few months, but as of yesterday evening, I can no longer play any of my files (which are TV / Movies) from my Apple TV.

Playback still works on my PC, Amazon Fire Stick, and phone - I'm even able to airplay my iPhone to the TV in question - but trying to initiate playback from the Apple TV is a bust.

I've tried restarting the NAS, updating Plex Media Server on the NAS, re-installing the app on the TV (and restarting the TV), all of which have had no affect.

Any ideas?