AVPlayerLooper error code "-12848"

implementing a video looper by following the "avplayerlooper approach" in the sample code found in the link below:
https://developer.apple.com/library/archive/samplecode/avloopplayer/Introduction/Intro.html
the following error occurs on random bases for diffrent devices with different iOS versions

NSLocalizedDescription: Cannot Open

NSUnderlyingError: Error Domain=NSOSStatusErrorDomain Code=-12848 "(null)"
the video formats we're using are : "mp4" "m4a"
and the assets are stored in .documentDirectory