Thank you! That’s exactly the information I needed.
The problem is not that you have a cached version of our certificate from before Monday—you have the current one, which is good until February 2022. Instead, the problem is that the your browser is checking the expired DST Root CA X3 certificate.
That issue is discussed at some length here. There’s nothing we can do about this on our end. The solution is to make sure that your browser and OS are current.
I think the reason this is happening now instead of on 30 September when the DST Root CA X3 expired is that our old certificate, which had that root certificate as part of its signing chain, was signed in the middle of September, before the DST Root CA X3 certificate expired, so was still good for about two and a half months after that.
A little more background:
And some advice for how to update manually if you’re stuck with something that no longer receives updates:
I’m having the same issue. I read the above solution and made sure my Mac & Firefox was current. When I just tried to download a For The People module I still got the same
“Did Not Connect: Potential Security Issue” warning and it will not let me override it.