I see that Cloudflare could solve this error, I rolled back the previous setting (with cloudflare dns and selfsign ssl) and still not see this issue again. :)
This error may be xenforo system, the member could insert their website link and this system redirected to their site and caused that error. Forum admin needs to delete that thread and remove the user posted that thread.
Sure it only happened on free versions, didn't happen with paid versions.
Maybe they want to people using free versions need to upgrade to paid versions for revenue purpose :D
My friend use a free cloudflare account with near 100 websites there but there is no one used paid versions, so I...
We solved this error, the guide is https://forumweb.hosting/21401-directadmin-and-cloudflare-error-520-web-server-is-returning-an-unknown-error.html
This error was from Cloudflare, but it can be solved by Directadmin and I still wait for directadmin if possible or from Cloudflare if they can fix...
We could solve this issue and there is a guide here https://forumweb.hosting/21401-directadmin-and-cloudflare-error-520-web-server-is-returning-an-unknown-error.html
I got this from Cloudflare, they are fixing, so we don't need to change anthing on the server, let wait for their fix but may be very long....
https://www.cloudflarestatus.com/incidents/hljt52nzcsnf?_gl=1*wespcs*_ga*NjkxMjY4NTQxLjE2MTMyMTI3Njc.*_gid*MTg5NTgyNDA1OS4xNjMwNDI5Nzg1
I have same problem here https://forum.directadmin.com/threads/error-520-web-server-is-returning-an-unknown-error-cloudflare.64448/
I think it came from clouflare and a part from directadmin, because I used letenscript (plesk onyx) or autoSSL (cpanel) with cloudflare then no problem at all.