FWIW, I'm also on Spectrum (by virtue of the Time Warner acquisition back in the day) and I get 10/10 on that page. That is, after turning off Firefox "Enhanced Privacy Protection" which actually blocked the page from loading at all for some reason. Got 9/10 using Chrome. Both on Linux.

Is it possible that you own your own router and have at some point configured the router to turn up 6 off? I know it is turned off on my router because I had some issues with Verizon ipv6 and tp link in the past.