Video takes 1-3 minutes to load/display during captions phase

Mac OS X
All latest browsers

Steps to reproduce:
1. Select upload video
2. Select a video to upload
3. Select "Captions File Upload"
4. Once on hold, try to attach a captions file, page is empty (see attached) and it takes between 1-3 minutes before video appears on page, browsers start to time out (see attached screenshot)