Safari could not establish a secure connection to Wikipedia?

I am trying to connect to Wikipedia.org using Safari version 10.0 (12602.1.50.0.10), on 10.12 (sierra) but get an error stating that "Safari Can't Open then Page", because "safari can't open a secure connection to the server". There is no padlock or anything else to try to get more information on the issue.

Trying in Google Chrome, "54.0.2840.59 beta (64-bit)", I am told that "Your connection is not private" and "NET::ERR_CERT_REVOKED". Clicking on the red warning symbol I get an indication that the "certificate issuer is invalid", with the certificate issuer being "GlobalSign Organization Validation CA - SHA256 - G2".

A friend on the the same local network running a Mac, with 10.11 (El Capitan), reports no such issues. I also see no reports on the internet, suggesting the problem is probably local to my computer.

Can anyone suggest a way to solve this issue?

Edit: seems like someone else is seeing issues with that certificate authority too, as reported on 'Stack Exchange'.