I can also echo and reproduce this issue with my GT-AX11000. Having two game consoles online. One gets OPEN NAT in the xbox game dashboard settings while the 2nd xbox game console gets either Strict or Moderate NAT.
For historical information, BigShooter started a post on SNB regarding at the time a RT-5300 which was mostly resolved by the installation of RMerlins 3rd party FW:
https://www.snbforums.com/threads/upnp-multiple-xbox-one-gaming-consoles-nat.35324/To which I also became apart of. I believe stock FW was never able to support OPEN NAT across multiple games consoles playing the same COD game which report NAT status as well. Unfortunately RMerlin doesn't support or develop his FW for the GT series of ASUS routers.
😞Thus I started this forum thread in regards to "NAT KIND" being used on various Mfr routers (FULL CONE NAT, PORT ADDRESS RESTRICTED NAT or SYMMETRIC NAT) and what seems to work and what doesn't work when having two or more gaming consoles online at the same time and achieving OPEN NAT across them all:
https://badmodems.com/Forum/viewtopic.php?f=6&t=21Between BiggShooter and myself, we have done extensive user testing with two or more game consoles.
There are a few routers that we can get OPEN NAT across the board if they are configured correctly and they do work.
Here are my recent experiences with the AX11000 router, this router being my first bought and kept ASUS router:
"Wire connected 2 xbox game consoles to the AX11000. Both here hard powered OFF with the hold and press of the front power button. Rebooted the router as well.
NetGear CM1100 cable modem.
OPEN NAT and Port Forwarding were enabled on the AX11000 router.
Turning on the first one, It reported Moderate NAT on dash board. I did the NAT Type Test on the 1st xbox and after it was completed, it now reported OPEN NAT. I looked at the port address and it was some 50K number. I was expecting to see 3074.
I turned ON the 2nd xbox console. It reported Moderate NAT on dash board. I ran the same NAT Type Test on the 2nd xbox and after it completed, it reported double NAT detected. It reported using some port address that was not 3074. I happened to go back in and set a manual port number and selected 50070 and applied the change. I ran the NAT Type Test again and now it reported OPEN NAT on the 2nd xbox.
I went back to the 1st xbox and ran the NAT Type Test again on it and after it completed, it reported Moderate NAT and Double NAT detected.
I went and ran a NAT Kind test from we certain web site and it reports that the GT-AX11000 uses Port Address Restricted Cone NAT. This is of course by default from ASUS. This also inhibits two or more game consoles from getting OPEN NAT while on line at the same time in some cases. Seem to be playing a small part in all of this oh this model router.
Hoping that ASUS or others can help with any kind of configuration to get OPEN NAT on multiple game consoles online at the same time."
I have since moved my 2nd xbox game console off the AX11000 router and on to a different router with a different WAN IP address so separately, both game consoles are getting OPEN NAT.
We'd like ASUS and Asus Engineering to review this and let us know what exact steps and configurations we can do with the GT-AX11000 router or any ASUS GT series router, to achieve actual OPEN NAT with in the networking settings for xbox, then also achieve OPEN NAT for the in game NAT status seen in CoD games when two or more game consoles are online at the same time playing the same game at the same time using stock FW.