Hello @Steve_Davies,
As @ged_hickman1 mentioned for Roon to operate properly, you would need to have the Core and the Roon Remote on the same subnet. Roon cannot operate properly over VPNs becuase VPNs often have limitations to multicast communication causing issues with our discovery process and our RAAT protocol. You can read the following thread where some users have gotten their setup working through a VPN but please note using VPNs is not officially supported by Roon:
Thanks,
Noris