Can't load certain websites and apps on my laptop and phone while connected to my xFinity router

Just as the subject says. I can not load certain websites on my laptop and I can not load certain apps on my cell phone while connected to my xfinity modem/router. 

Just a little background:

1) I have a netgear router connected to the modem. I only use this router to connect to a system via ethernet cable that gives me updates on solar panels I have installed on my roof. I tried connecting that system directly to the back of the Xfinity moden, but for some reason the xFinity modem blocks the system and I was unable to recieve updates, so I solved the problem by using the netgear router instead.

2) This xfinity router/Netgear router combo has been working for a year and just not started giving me and everyone in my house problems. Certain apps and certain websites just wount load! This is rather frustrating.

    a) Apps and websites that wont load: Twitter.com, Reddit.com, Amazon.com, http://portquiz.net:81/, xFi mobile app, twitter app, reddit app

     b) Apps and websites that will load: Youtube.com, Google.com, fourms.xfinity.com

3) At first I noticed that my netgear router was not connected to the internet for some reason, even though it was connected via ethernet cable and has been working just fine from 2018 to 2019. Once I reset the xfinity modem, I was able to regain internet connectivity on the netgear router. 

       a) Connecting to directly to the netgear router did not yeild any problems as I was able to load the previous websites that I was not able to while connected directly to the xfinity modem. 

4) Traceroute while connected to the xFinity modem to the websites I couldn't connect to timed out all 30 hops. 

How do I fix this as the xFinity folks over the phone just keep resetting my modem, which hasn't changed anything. 

I know people have been contacting  @ComcastJohnN