This only happens in the iOS version of YouTube (YouTube app). The app has had a bug that when the video being watched catches up to the end of the buffer point. It is very frustrating. The best workaround is to use the mobile version of YouTube. In Safari, go to YouTube.com and save that page (it will be the mobile version) as a home page icon. Use that whenever looking up videos. It also has a button that allows you to select between HQ (high quality) and normal versions of the video. I have found that with most videos the normal version looks good and load much faster. Either way it gives you options. The only bad thing is if you are clicking a link from email, safari, txt, etc. the iOS version loads the video instead of the mobile version. The workaround around for this is as soon as the video loads in the iOS version then press the bookmark icon (the icon that looks like a book to the left of the play button) and close the video. Now go to the mobile version (the icon you saved to your home screen and it will be in your favorites list. The mobile version blows away the iOS version.