Hi @mrdave,
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.
These previously showed up in Roon, correct? Have there been any changes to your setup?
Since experiencing this issue have you tried rebooting your Core machine and networking hardware?