Hello @Carsten_Boisen, and welcome to the community! Had this device worked without issues previously? Have you tried entering the IP address of your core using the “Select a Roon Core>Help” screen?
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.