It turns out the problem was simply related to my DNS settings for that WiFi network. Cox's default DNS servers are 68.2.16.25 and 68.2.16.30. I had overwritten these setting with 1.1.1.1 and 8.8.8.8.
Why was logging into Cox a problem?
Because I needed to sign in through Cox’s captive portal. To do that, my MacBook Pro had to be redirected automatically to Cox’s login page using their own DNS servers. Until I authenticated, the hotspot intercepted my network traffic and restricted Internet access, redirecting web requests to the captive portal so I could complete the sign-in process. But since I was trying to use non-Cox DNS servers, this process failed.
