Today 2018-09-27 I’ve got 521 error on domain kuda29.ru. Web server was running. There are several sites correctly working on the server, but only this domain is under CF and returning 521 error.
Domain started normal work only when I switched Status on DNS page to “DNS only”.
I’ve got an answer from my hosting company:
From the server side there is no restrictions to any of CF ips. From what ip CF has made requests to kuda29.ru and what response was from the server?