On behalf of the team, please accept my apologies that it’s taken us this long to reach your request for support. We’ve prioritized this thread and will be responding more promptly moving forward.
With a multi-router setup such as the one you’ve shared in your initial screenshot, you’ll need to check the following:
UPnP is enabled on the router directly upstream from your Core; in this case, it’s the first RT-AX86U. I’m assuming it’s enabled, as the port test came back positive.
The port listed in Roon → Settings → ARC (in your case, 55002) matches the port assignment in any manual configurations you’ve set in your router web GUI’s. If you have set manual rules for ports, make sure the same port matches in each router, including your modem/router.
Have you double-checked any firewalls and security exceptions on your Core and each router?
It’s always very possible that China Telecom has some form of carrier-grade network address translation preventing your Core from connecting. However, as far as I know, some China Telecom users are still able to configure port forwarding under certain conditions for gaming and livestreaming. Do you know if you’ve been provided with a public-facing IPv4 address?