Server Version#: 1.25.5.5492
Player Version#: 7.28.1 (iOS)
x265 movies only have sound when played on iOS or AppleTV. iOS only shows the cover art while AppleTV shows spinnning animation. Already restarted Plex server and the NAS (Synology DS1520+). Same movies play fine on Firestick 4K and Shield.
Playing x265 TV shows have no problems. Had to re-download x264 copies of the movies to be able to watch.
I just solved the issue on my Apple TV. I was able to play x265 movies from the VLC app. This told me that the issue wasn’t PMS. It was the Plex app on the Apple TV.
I deleted the Plex app and re-installed it. Movie playback is fine now.
I would expect that these steps will need to be repeated on each device that you have on iOS.
Similar trouble with x265 on IOS. Watched entire season of Ozark Season 2 4k HDR no trouble. Went back to play an episodes few days laters now constant stuttering on every episode - but audio plays fine. Nothing changed except probably update. Nvidia shield works perfect.