Can't Reach This Page, then fixes itself after a second

What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

Does this happen on all devices connected to the router? 

Happens with different browsers? Try MS Edge or Firefox or Opera?

Try using alternative DNS like Cloudfare or Quad9 on the router. Apply the changes and reboot both router and PC.

Try disabling IPv6 on the router?

Has a factory reset and setup from scratch been performed? 

FYI, this router is EoL so use as is or may need to find something newer:

https://community.netgear.com/t5/Nighthawk-Wi-Fi-5-AC-Routers/Top-NETGEAR-FAQs-Support-and-End-of-Service/td-p/1881104/jump-to/first-unread-message