This seems to be a device specific bug on only iPhone 6S Plus.
Steps:
AVPlaye
My suggestion would be that since your use case is an animated loop to ditch the AVPlayer and use a UIImageView.
UIImage
has animatedImage(with:duration:) where you can input an array of images and animate them how you like.
I think this would solve your problem. In my experience AVPlayer has been a little wonky with iOS 10. I think that since you are only seeing this problem on the 6s+ and 7s+ is proof that it has some issues.
If you are absolutely committed to figuring out the AVPlayer, first submit a bug report to Apple. Then maybe try adding a UIImageView behind your AVPlayer that has the image set to a blank frame from your video. This is kind of a hacky solution, but it might work. Additionally, check out this stack overflow post. It might shed some light on the issues you are having with the AVPlayer.
Best of luck.