Here's the log.
Turned on debugging.
Rebooted.
Played a TV episode.
Subtitles were off.
Turned on subtitles.
Selected "Set as default..."
Confirmed that request.
Selected Close.
Subtitles worked as expected.
Played video for a few more seconds.
Stopped video.
Restarted video subtitles didn't display.
This happens all the time for any video.