Not sure if you’re checking Twitter these days, but looks like the SSL certificate you’re using is invalid at least according to some browsers.
Thanks for reporting, @pleary! Yes, the SI sysadmin are looking into it. Something went awry with our last cert update.
Those certificates are sorted out now; thanks again for reporting!
This certificate is really very helpful for all the websites. As I am new in this platform I was not so familiar with what is an SSL certificate. But after applying this to my site, it provides the best security to my site.