iOS AVPlayer crashes (sometimes)

I have a very strange problem with AVPlayer. I am using this player to play videos in my iPhone iOS application.

At first look it seems to work fine. But there is some videos on which player crashes. What is strange, that after this crash, other videos fails to load or crashes, even if I kill application. To fix this I need clean install application each time after video player crash.

What is more strange, that sometimes problematic videos stops to crash and play normally.

To save video files I am using Amazon S3 web-services (I am taking videos from there).

Does anyone know, where the problem could be?