Sounds like it could be that Plex is transcoding those videos in particular for some reason.
There is a hardware transcoding bug where some clients play the transcode (web client, iOS) and some don’t.
Seems like most of the recent problem posts with Shield as a server are related to this… https://forums.plex.tv/tag/server-nvidia-shield
Specifically: Shield tv don't hw transcode
Try turning off HW encoding in the transcode settings on the server’s web page.
Also, you can see if it’s decoding and encoding on the dashboard web page or serving the original…
Just audio in SW…
Video decode in HW encode in SW…
Video decode and encode in HW…
This last one works in the web player, but not in Android apps.
