I am also getting these issues.
Doing a search on the forums, it seems many people have reported this issue, but it has never been resolved.
PMS on Nvidia Shield Pro (2019)
DVR Recording
Closed captions show as available (DVB_TELETEXT)
Once selected, the playback will crash.
Nvidia report that they have raised this issue with Plex back in January of this year:
https://www.nvidia.com/en-us/geforce/forums/shield-tv/9/291531/closed-captions-not-displaying-using-plex-media-pl/
This post in the forums listed the error logs, showing the issue, but he didn’t even get one response:
When will this bug be fixed? I think I will get my recent Lifetime purchase refunded.