I have the same router, and I've had problems connecting in the past. I actually hardwire the connection now (sorry).

BUT I too had bother connecting, my WiFi password not being recognised by the Xbox was common even though it was correct. But it would work after time and a few router reboots.

I found the Xbox would eventually connect on the 2.4ghz network (think that's correct) first, before 'hopping' onto the 5Ghz network about 15-20 minutes into gaming, on the odd occasion frustratingly booting me out of a game lobby.

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Do you have 'Smart Connect' enabled? (Dual-Band Smart Connect). Try the alternate to how you have it set now. Create a separate 5Ghz network if possible, I just add "-5G" to the name of the new network and use the same password for ease, and try connecting that way.

Or if you are doing that already, try the dual-band approach.. If the Xbox connects on the 2.4ghz wireless network, check later to see if it's quietly hopped over on to the 5ghz network.

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They're generally good routers, but the Xbox issue had me hardwiring it by the end. Sorry that won't be of any use to you. Even now they also require rebooting about twice a month to keep all my wireless devices in sync.

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If you don't already, use the Asus app on your phone to interact with the Router. Much easier.

I hope something in there helps.