I re-installed 6.2.3.2 and downloaded one of the exact same episodes; captions are playing perfectly fine on my RokuTV.
maribeau
Then it's caused by this change:
[quote]StreamFab 6.2.3.3 Changelog
Fix: A problem that some double-line subtitles only display one line when downloading videos from Netflix.[/quote]
I can't test with RokuTV - but you can try with Preferred Setting
Subtitle Action: "Extract Original Format" to get *.vtt from NF
and convert to *.srt with SubtitleEdit or similar tool