Subtitles format for HLS Stream

I am looking into the “simplevideoplayer” sample provided by ROKU SDK and found issues with Subtitle support. When initially loaded the app into my ROKU player, everything worked fine and I was able to see the subtitles.

Then, I updated subtitle file (craigventer.srt) by removing subtitles for few timelines & editing few words. After that, the player stopped showing subtitles. I am using Notepad to edit/update SRT file.

Is there any specific file format in addition to general SRT structure?

Thank you