Hello @xred,
Thanks for contacting support regarding this issue. VPNs are known to cause issue with multicast and our RAAT protocol and as such, we do not officially support VPNs. Generally speaking, when you use a VPN this causes the device to use a different subnet than the Core.
There have been some users who have managed to get Roon to work through a VPN (Remote connection via VPN - [Resolved] but ongoing discussion) but it has required special settings to be made and is not officially supported. I hope this helps, but please let me know if Roon does not appear to be working as expected without using the VPN.
Thanks,
Noris