Certain sites will NOT load while being hardwired to the internet

So I'm having this weird issue here. Certain websites will NOT load while being hardwired to my Xfinity modem/router, but if i unplug it and use my computers wifi, then there are no issues at all.

Facebook, Instagram, Twitch, are the main ones that will not load while be hardwired plugged into the internet, but then unplug the cable... turn on wifi... and it works 100% . 

I just got a new modem/router from Xfinity 2 weeks ago and still the same issue. 

I've also gotten a a few new CAT5 cables as well. 

I've also turned off and on the advanced security in the Xfinity App. 

When i do a speed test im getting about 960mbps for my speed.

Any help here would be appreciated. I spoke with an Xfinity rep and they couldn't figure it out.