Based on your feedback, I'm going to say that this was a localized issue that we have no control over. It's very possible that there was some MIM issue that broke the security chain from that WiFi network and TAG. Your browser acted correctly in the case that the chain was broken...
This is also a very plausible answer to the issue. If the time/date is out of synch by a certain threshold, this will cause security errors as well. A correct date and time is needed to establish and maintain a secure connection.
Thank you for taking the time to give us the feedback for evaluation!