Some websites won't load on my network. Netgear LB 2120

Hello all, 

Recently I've been having an issue where several websites won't load. Some websites load fine and I'm able to stream videos and play games over the internet. The error message I get changes but is usually "ERR_CONNECTION_RESET". I have tried the same web pages on two different laptops and two phones connected to my WIFI and it's the same story on all of the devices. The phones and computers load the websites fine if they are on cellular data or the laptops are using the phones as a hotspot. I have eliminated the router as a possibility by connecting directly to the modem via ethernet cable and I have the same issues. I have also tried three different SIM cards from two different providers and that hasn't changed anything either. I have also done a factory reset on the modem with no improvement. My SIM providers have done all the testing on their side and say everything is normal for them so it is likely the modem. I'm out of ideas. Please help. Thanks in advance.

-Nate