Depending on what router you are using, especially panoramic there might be ad blocking turned on and that might be blocking the site because it has an adserver running with it. Common on mesh networks.

I had the same issue with another provider when I was trying to use Paramount+ turned off the ad block on my network and it started loading as normal.

Just a suggestion as there would be much more info on that if Cox was straight up blocking the app and I couldn't find this through an quick (even though not through) Google search. Seems like something a lot of people would have an issue with.

Could always bypass the router and go direct to modem to test that.