Subtitles appear and immediately disappear

[shadowfax2112]

Jellyfish 12.1 server I have this issue when watching videos using the web player, Infuse or SwiftFin. 

When watching the video a subtitle will appear on the screen and then quickly disappear before it can be read. 
Jellyfin indicates it is serving the video in direct mode.

If I open the video from the filesystem with VLC the subtitles appear as expected.
I have also installed and ran the subtitle extract plugin with no change.

There is very little CPU usage on the server.

Any ideas what I can change to fix this behaviour. 

Thank you!

[TheDreadPirate]

What kind of subtitles are they? Can you share the media info or ffprobe output for this file? Does this happen with EVERY video? Or only videos with a particular subtitle type?

[shadowfax2112]

I could have sworn they were SRT but they are Tx3g.

[TheDreadPirate]

I have never heard of that subtitle standard.....

And you confirmed that only your files with this subtitle type have this problem?

Apparently we do support that format, in our docs it's labeled MP4TT/TXTT, but only when in a MP4 container. Are your files MKV or MP4?

[shadowfax2112]

It is an m4v file. Video files were converted from initial format to m4v with iFlicks as I was using my macOS TV.app for watching videos previously which required Apple Formats. I will play around with converting to MP4 which is very similar to MP4 and converting Subtitles to SRT.