All of my websites are working great through CloudFlare, except one…
On the non-working site, the domain and sub-domains return “Error 521”. If I turn off the Proxied option in DNS, or if I specify my web server’s IP address in my hosts file, it works fine, but not through CloudFlare. All of my other websites are hosted on the same server. I have firewall rules that permit all CloudFlare IPs. Even if I open up port 443 to the world it still does not work. CloudFlare thinks the website is down but when I test it manually, it’s not down.
I removed the domain from CloudFlare then a few minutes later added it back, but that did not help.
What else should I look for to fix this issue?