Error 521 with proxy

i have a server on premise, with a proxyed DNS entry on Cloudflare.

For a week or so, when users try to connect to my server they have a 521 error, but if refresh a lot, the browser reach the webpage.

I don’t understand why, could you help me ?

For precisions : Cloudflare’s IPs are already whitelisted, and the server is up. The same problem appears on securityheaders"dot"com when i scan my uri, sometimes it shows me a F with none of my security headers and sometimes it shows a A+ with everything i have set.

Thanks a lot for your help.

This topic was automatically closed 15 days after the last reply. New replies are no longer allowed.