Steps to reproduce:
1. Navigate to moodle
2. Use example files I have attached to this bug
3. Click 'Add an activity or resource'
4. Select 'file' from the list of options under Resources section
5. Upload files (html and vtt files)
6. Save and view added content
Videos play without the ability to toggle closed captions.
Videos play with the ability to toggle closed captions on all version of Internet Explorer.