Plex Watch Later Not Working Anymore

I am running Plex on my Tivo Roamio 4 tuner, and everything is working fine except for the "Watch Later" feature. I have no problem adding videos to the queue through my browser, but when I try to watch them through the Plex app on the TiVo, I get an error message: "There was a problem playing this item. The video did not start playing on time." This was working fine a few days ago. I have tried turning off SSL and rebooting both the Tivo and server with no luck. Anyone have any idea what could be happening? Thanks!