While it's not a cache issue, I have the same issue on 3 different devices at home and the office.
You did help point me in the right direction. By cleaning the cache I got a new screen.
"This site could be risky".
"Advanced security blocked access ".
I went to Xfinity and reported it. Hopefully they will release it.
I noticed the issue first at my office. A couple of months ago. Right after they installed a new router. As I type this I realize that a week ago we put a new booster on our home network.