Some other user reported that same thing this morning but I couldn't find any explanation to this err. It basically works for everyone except for these two precise cases. One idea I have is that you might be behind some sort of firewall that's blocking my website (because in the past either the IP or the domain got flagged by some antivirus company and now some business networks block it) – might this be the case?

When reporting this, it's useful to include your browser and exact version number. Most browser ship updated SSL cert packs with new versions, and debugging can be hard without this information.