What’s the website your getting this error on? Also is “always online” mode on because if so it should still load an un-cached copy of your website. Also, I’m sorry to hear your getting the 521 error, check to see if Cloudflare IP’S are allowed to bypass or allow in your firewall settings. A list of Cloudflare IP’s is available at IP Ranges Also the cause of the 521 error? Error 521 occurs when the origin web server refuses connections from Cloudflare. Security solutions at your origin may block legitimate connections from certain Cloudflare IP ranges
The two most common causes of 521 errors are:
- Offlined origin web server application
- Blocked Cloudflare requests
I hope to hear back from you soon!