Have you tried a hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons?
In addition, Apple not do anymore updates for iOS 9, now that iOS 10 is out!
Also, if your iPad is an iPad 2, 3 or 1st gen iPad Mini, iOS 9.3.5 is your last update.
So, if you are having troubles using Apple branded apps to view your videos and they aren't working, you'll need to find an iOS 9 compatible third party video that will play your hi res, 4K, 60fps videos.
There will be NO MORE SUPPORT or help from Apple for iOS 9.
If your iPad is newer, I recommend upgrading to iOS 10.
FYI, iPad 2, 3 4 and, I believe, the 1st gen iPad Mini and Mini 2 were not capable of any 4K video playback, natively.
Older iPads, at best, can only playback the .mp4, 720 or 1080 format at 30fps.
Newer iPads, (iPad Air, Air2, Mini 3 and 4) are the only iPad models capable of playback of 4K videos and, once, again, only at 30fps, natively, and NOT 60.
Look to third party video playback apps that work with your year, model and iOS of your iPad and that will support the much higher frame rates.
Good Luck!