please help i asked earlier and still no response
What kind of files are they? can you attach the Plex Media Server.log from when you start playback?
360 app settings you can enable debug logging which will include the 360 app logs into the server logs. https://support.plex.tv/hc/en-us/articles/201643703-Reporting-issues-with-Plex-Media-Server
I have a similar issue. My XBOX 360 will play music without issues, but some video files continue to load, but never play. This is not specific for a file type, as some .mkv files will play but others don’t. The same is true for .avi and .mp4 files.
it might not be about file type but still need to see server/360 logs to even begin trying to figure out what might be wrong. if you want an off hand guess I’ll say that streams need to be transcoded and the server is to slow when doing so.