Hey @Espen_Evensberget,
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.
Has the Chromecast device ever showed in Roon, or is this a new behavior?
Have you tried rebooting your Core machine and the Chromecast?
Thanks!
Dylan