Hi @Dean_Kimball,
I should have mentioned it, so forgive me. Autoconfiguration won’t’ work in a full IPv6 environment, since there’s no port forwarding service for UPnP/NAT-PMP to negotiate.
The first test would be to remake any IPv6 firewall pinhole rules pointing to the IP address of the RoonServer machine.
This diagnostic, however, suggests you’re still in a mixed router setup and the downstream router is managing the address allocation for the RoonServer using unprefixed IPv4 addresses. In this setup, this would place you behind a wall of NAT in an IPv4 environment.
What IPv6 setting do you have toggled in the ASUS router currently, if that router is still involved here? I recommend testing with Native or Passthrough.
If that doesn’t help, are you in a position to temporarily disable the ASUS router and allow the Starlink router to manage the network fully?