Problems with files playback start. Jump forward helps

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I have a small but annoying problem with the Emby Server using Apple TVs for playback. 

When i start a movie it shows a black screen and is loading but doesn´t play the movie. When i press forward it plays the movie perfectly. It is on every of the four Apple TV devices, so i assume the emby server is the issue. I also changed the NAS device (but not the HDDs) and i reset the Apple TV.  I also changed all the Video format. 

The same config works perfectly in other locations. 

My assumption is that theemby Server at the NAS has any corrupted file in the config or similar. When i uninstall the emby server it keeps all the settings and libraries and so on. So this doesn´t change anything. 

 

Can anyone help me with this? 

 

 

Background: I work for a company which build tour busses and we have been using this configuration for several month now.