I am seeing the same issue, on a MacBook with both Safari and Chrome, both of which I have flushed the cache. I get logged in and redirected to ; https://tv.xfinity.com/adding-device
That is a black page with only the top banner populated - Comcast logo, Language selection, Social media links - and the rest of the page completely blank. Refreshing this page goes to a blue background page with "Xfinity
Now connecting to your entertainment experience" and the three pulsating dots ticking indefinitely. This has been happening for at least 4 days.
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