My test server is in the US and Let's Debug / Encrypt will try from various points of the globe (some in US). This free test (here) shows no success from any of its 5 world regions with HTTP but all 5 work for HTTPS (try it with http://gollum.at for example)
This looks like a geographic based firewall to me. The only puzzle is how you got a fresh cert given what I see now. HTTP must have worked for that. Or, did you use the DNS Challenge for today's cert?