Same problem. I contacted the admin via PM and explained that despite setting my firewall to allow l2topzone's new web host IP to connect to the server, it still shows the server as offline. I'm absolutely positive I have the correct settings because I only changed the IP in my server's iptables settings. It worked fine with l2topzone old IP.
In fact I can't even detect any attempts by l2topzone to connect to the server at all. I could detect that before whenever I pressed the check status button, and I can also detect the incoming connection whenever I press the check status button on hopzone.
In short, it doesn't seem to be a problem on my end, but something to do with l2topzone new webhost. I hope this will be reviewed more seriously soon, because we're dropping % of server uptime status, as well as losing vote counts. Please do not respond again by saying "see it works for most servers so the problem is not on our side", because apparently it is.