@MagnusAusar
Hello,
Please refer to the below troubleshooting guide to check some basic settings again:
Why port forwarding feature is not working on my router?
If still no help, please provide the below details:
1. What is the WAN IP address of the A20? And what is your detailed network layout, how are the modem and routers are connected?
2. Ensure the IP address for the Xbox One is in the same IP subnet of the A20, that's to say, if the default IP address of the A20 is 192.16.8.0.1, the IP for the Xbox One should be 192.168.0.x, please confirm this on your Xbox One.
3. Use the WAN IP+port number on a LAN PC to test if the port is opened. If this access failed, it might be your ISP has restrictions on the port/service and you need to confirm with this. Additionally, we strongly suggest you turn off the firewall on the Xbox One as some devices' firewall blocks connection from WAN by default.