I've just replaced my netgear nighthawk x6s, and my gateway is/was fine on my unit. That being said, the most recent firmware is currently broken and old (in true netgear fashion), so perhaps it is a problem if the router has a new firmware update.
I did upgrade, then downgrade the firmware before I boxed it up and replaced it, however but both versions are not new releases, by far.
Maybe push a pin in the reset button and see if it returns.
ipconfig /all (in a cmd prompt should show your current gateway)
Best of luck!
I had the same issue with my ageing r8000p, just before I got rid if it. The firmware has been broken for that unit for years and they never bothered to fix it. Just pushed out a beta which I refuse to use especially on a Internet gateway.
I got around the dns failure by setting the IP on the laptop it was hardwired to.
IP 192.168.1.100 Subnet 255.255.255.0 Gateway 192.168.1.1
Dns1 8.8.8.8 Dns2 8.8.4.4
I then pushed the hardware reset button with a paperclip at the back of the router.
As soon as the led showed a lan wire connection, I punched 192.168.1.1 in a browser bypassed the wizard and selected manual setup this got me back into the GUI, I went straight to WAN setup and saved the dns settings (above) into the router.
For some reason, the factory reset blanked them out entirely. Then, it was just a case of entering the isp username and pass (which I didn't bother with as after a firmware downgrade then upgrade I decided... I, too, was done with netgear)
I bought an Asus gt-axe16000 to replace it with. The only netgear thing I own now is an unmanged network switch lol.
Best of luck. I hope you get it sorted