I’ve experienced this. I’ve also had it play movies infinitely on repeat, or infinitely play the last episode of a season until I stop it. Sometimes it just likes to pause at the last second of video and stay there indefinitely. The Shield app is a complete mess.
I have this exact problem as well. I noticed that if I press home during the post play screen (or up next screen), somehow it still plays in background even if I’m not on YouTube app.
I haven’t confirmed it is exactly this as it’s happened many, many times over last few weeks. But I’ve also noticed sometimes the video never goes to the “up next screen” and just freezes on the last frame, so…who knows?
I noticed a similar issue on my android tablet and Google TV chromecast. That when I watch a show in a series I’ve already watched with the auto play next as disabled, Plex marks the next episode as recently watched. This seems to be due to the fact that while on the up next screen plex has the next episode as paused with 0 sec played.
Since the episode is “paused” this also seem to be disabling the screen timeout function which kills the battery on my tablet if I fall asleep or walk away.
I’ve noticed this because I use the recently watched section keep track of where i am on my series I’ve already watched.
I don’t have this issue with my roku, openPHT. or PKC only the android players. But then again openPHT and PKC don’t use Plex’s Up next feature.