Since this is about Plex App 2.18 on AppleTV HD 4K
Since you fixed this big in 2.14 and it is back in 2.18
see this link and read the last line of bug fixes…
the last line read " * The library view with an unplayed filter wouldn’t reload correctly when marking something as played."
Both app and server are up to date on AppleTV 4K with latest tvOS (currently on latest GM released today) and PMS updated recently (1.19.3.2793-36efde971) on macOS (iMac 5K)
