Same issue here, I transcode video similar to you with Handbrake to mp4 with H264, level is usually at 4.0 and Audio is always converted to AAC. The video is stuck at buffering, and if waiting long enough, either the app shows
Playback Error:
An unexpected playback problem occurred.
or the app crashes completely and PlayStation shows the following error:
An error has occurred with the application: (CE-34878-0): Plex
I noticed the issue shortly after the PlayStation update to 11.02 and Plex App update (from the PlayStation Store) to 3.00 back in Nov’ 2023, and it has been like this ever since. I tried reinstall and reset of player and server as well. Movies play perfectly fine with other players.
Server Version#: 1.40.1.8227
Player Version#: 5.80.0
I’d be happy to share server log files if it helps.
I have already commented in another thread, where some people mentioned this issue as well, calling it the „yellow ring of death“. Some people were able to fix it by disabling direct play on server side, which forces transcoding. But my server does not have enough cpu power for transcoding, so it is no solution for me, but it might be something you can try.
Regarding Plex‘s support, I got a reaction on my comment, where a Plex Employee suggested to update to the newest Firmware (Wich I already had and after which the issue started in the first place), but unfortunately that is all I got, no follow up.
My current workoround is moving the Chromecast to the device I want to watch with. Might have to buy another eventually. But the best case would still be that someone from Plex would look into this and resolve it. My hopes are still up ^^