EAX 18 (AX1750) won't pass some web sites.

I have had this extender for about 8 months now and it has never worked right. I have been using a work around of using the devices LAN port to connect to my PC more or less like an expensive WiFi adapter. I am able to connect and setup the extender and transmit the internet signal from my router but it blocks about 25% of the Web sites. I first tried to use the customer support (90 days free) and they were no help at all all I kept getting were instructions to reboot reset etc. from an obvious decision tree they had on their computer. They could not understand what I was talking about let alone give me a fix after some hours of frustration I just gave up and have used the LAN port work around ever since . It actually gives me good throughput about 300 mbs on a 800 mbs cable internet connection so I didn't send it back. I have seen many complaints about the same problem on the net with no definitive solution. (DNS, DHCP, port forwarding tried them all)

I have a ISP supplied (Comcast) modem/router Ardis model AR TG3482G. This modem has been locked down by Comcast so that only a few parameters are actually available to change  since modem management is through your account in the cloud and no longer locally modifiable.