ARC showing as Ready is a good sign, so this looks like a case where the app is up but remote access is not actually making it through from outside your network.
Since you’re on a mesh setup with multiple routers, the two things we usually need to confirm first are whether ARC has a working port forward and whether the Roon Server and the router managing internet traffic are on the same local network path. Our guide on how to know if your devices are on the same subnet/IP range walks through that check, which is especially useful on mesh systems.
To narrow this down, could you send us:
Whether the issue happens on cellular data, WiFi away from home, or both
The exact error message ARC shows, if there is one, or a description of the current behavior
Please let us know what you’re seeing and we can continue from there, thanks!