Roon Arc connection ClientUPnPError - ConflictInMappingEntry

[Rugby (aka Daniel or Big Dan)]

Tailscale implementation with ARC to circumnavigate ISP CGNAT

In case you are currently unable to use ARC because you can’t forward a port due to your ISP using CGNAT (Carrier Grade NAT). A free solution is available that should suit most Roon users via one implementation or another. The basis of the solution is that you run app on a machine in your local network which communicates with an app on your phone. The app on your local network creates a 'subnet router’ which allows your phone to behave as if it is still on the home network when you are mobile. …

The above might be helpful. Keep in mind that you cannot be using Rock or a Nucleus as a core as you have to setup the VPN on the Core machine. I just noticed that you are using a QNAP as a core, so there maybe a Tailscale QNAP app.