My name is Timoor Kurdi and I’m a Support Engineer at JW Player.
Could you please follow the instructions on this page so we can try to reproduce the issue? – https://support.jwplayer.com/customer/en/portal/articles/2186238-troubleshooting-%E2%80%94-creating-a-reproduction-page
I was able to make the CC work, the issue was a No ‘Access-Control-Allow-Origin’ header issue coming from https://d24tcib9e8meg9.cloudfront.net/media/captions/telephants-dream-subtitles-en_uPPhxHZ.vtt. This is done by browsers for security purposes and has to do with CORS.
Crossdomain/CORS is a web based security feature that prevents certain accessibility to web content. In order to allow access, you need to instruct your web server to allow access to the content. This occurs in either a crossdomain or CORS file. The following article goes into great detail about this: http://support.jwplayer.com/customer/portal/articles/1403679-crossdomain-file-loading
The web server hosting the content sets the headers, if you host with JW Player we ensure that everything is CORS compatible otherwise you have to ensure a relative path to the file and host the vtt file locally.