Have you, or are you willing to, turn off xfinity's "Protected Browsing"?

I think if you browse to this url you can turn it off https://internet.xfinity.com/network/protected-browsing

Or via the app:  https://support.simulationcurriculum.com/hc/en-us/articles/360046008614-How-To-Disable-Comcast-Xfini...

I've pushed the release of the new certificate that should address this to Feb 24th. I did not want to risk some unforeseen issue breaking things right before EF Go Live.  

If turning off Protected Browsing doesn't work or is not a palatable solution, I might be able to figure out a work-around.