Hello @Alex_W 

Thank you for posting on the TP-Link Community.

How is the AX21 connected and configured? Is it connecting to the ISP modem via WAN and using Dynamic IP? Please be sure the WAN IP address is a public one, then you can try to open some necessary ports requested by the Xbox or game service as follows:

Port forwarding: how to set up virtual server on TP-Link wireless router?

From the Xbox website you'll need these ports opened on your router:

"These ports must be open to connect to the Xbox network:

• Port 88 (UDP)
• Port 3074 (UDP and TCP)
• Port 53 (UDP and TCP)
• Port 80 (TCP)
• Port 500 (UDP)
• Port 3544 (UDP)
• Port 4500 (UDP)

Note Some game developers require you to open additional ports. You should always check the game developer's website to see if the game you're playing needs additional ports to work."