Though I also tried setting up googledns in the router and it did not fix the problem
I am having trouble accessing my sons school grades login webpage. This started when I had an older wndr3700 in place. Thought something had failed so so put in a dlink dir 600L that fixed the problem but would not support two Xbox live connection. Just installed a tp link archer c7 and the website problem is back again. Every device behind the router cannot connect to the website. Connecting my laptop direct to the modem works. Putting a computer in the DNS does not work. Turning off firewall does not work. Setting up a proxy on my iPad does work. What else could I try? Is there a way to setup a proxy connection when the computer accesses just that site?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic