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.
Is there any change after a reboot of the Core machine?
Is there any change in behavior if you reboot Roon Server via the Antipodes Web Interface? You can access the Web Interface by putting the IP address of the Antipodes in a Web Browser and then navigating to Apps -> RoonServer -> Restart Roon Server.