Hi @Ralf_Schafer,
So we can better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
Where is your media stored?
Can you share a screenshot of the screen after you click the blue spinner as well as a screenshot of Settings > Storage?