AVPlayer playerWithPlayerItem deadlock - ios

Question

I'm using Apple's AVPlayerDemo in order to playback video files (the videos are .mp4 coming from my Amazon S3 server).
The player is a subview of a custom table view cell, and the user can scroll the table to switch between videos (an players). There is no simultaneous playback, the player is deallocated on the 'didEndDisplayingCell' method.
The problem is that there is a deadlock after several scrolls (the number of scrolls before the deadlock varies, but eventually it always happens).
the deadlock is on this line (running on the main thread):
[self setPlayer:[AVPlayer playerWithPlayerItem:self.playerItem]];
It seems that playerWithPlayerItem is on mutexwait, waiting for a background thread.
Logging shows that the dealloc of the former AVPlayerDemoPlaybackViewController is called before the deadlock. here is the dealloc code:
if (self.player) {
[self.player removeObserver:self forKeyPath:#"currentItem"];
[self.player.currentItem removeObserver:self forKeyPath:#"status"];
[self.player pause];
[self.playbackView.layer removeFromSuperlayer];
[self.playbackView removeFromSuperview];
self.player = nil;
}
The view controller's player property is nil before it is assigned by the dead-locked line.
The dead-locked line is called from this block:
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:mURL options:nil];
NSArray *requestedKeys = #[#"playable"];
/* Tells the asset to load the values of any of the specified keys that are not already loaded. */
[asset loadValuesAsynchronouslyForKeys:requestedKeys completionHandler:
^{
dispatch_async( dispatch_get_main_queue(),
^{
[self prepareToPlayAsset:asset withKeys:requestedKeys];
});
}];
Here is the threads state at the time of the deadlock:
Please advise - thanks!!