R8000 HOW DO I ROLLBACK THE FIRMWARE VERSION??

I know this is too late to help the OP, but...

I ran into the same problem.  Some firmware update completely screwed up my R8000 router that had been working fine.  I was ready to throw it in the trash.  Every device on the network was having problems getting to sites.  Bypassing the router's DNS by using VPN told me that it was the router, not the PC.  I tried different DNS settings on the router but that didn't help.  This is a Netgear problem that should have been resolved already.  I'm not impressed.

Anyhow, what finally worked for me was to go to the IPv6 screen and set it to "Auto Detect".  When I did that it set it to "Pass Through".  So far, after a couple days I've had no connection problems.