There’s an issue with autoconfiguration for Starlink residential WAN IPv6 addresses. The prefix handling differs between Starlink’s implementation and RoonServer’s handling, kicking an invalid IP exception.
This is a longstanding issue that, fortunately, is finally nearing resolution, as the ticket has progressed from QA to our developers to implement a fix. The good news is that you can expect RoonServer and Starlink IPv6 addresses to function shortly once we’ve merged the fix into a release. This will likely be in the next several releases, but we don’t have an exact timeline.
The bad news is that you will need to use an VPN or proxy server to bypass Starlink’s WAN IP in the meantime. Most users on this forum have found success with Tailscale as a workaround in your exact situation: Tailscale implementation with ARC to circumnavigate ISP CGNAT
ARC With Starlink & Ubiquiti UniFi Dream Machine [Ticket In]