Plesk domain served by CloudFlare shows 522 error Connection Timed Out

Symptoms

• Site served by CloudFlare shows:

  522 error
  Connection Timed Out

  or:

  ERR_CONNECTION_TIMED_OUT

• If site is resolved to a Plesk IP in the hosts file (without CloudFlare involved into processing the request), it displays correctly.
  Or, it may show SSL warning:

  Your connection is not private
  This server could not prove that it is example.com; it's security certificate is not trusted 

Cause

CloudFlare blocks connections to sites with untrusted SSL, or domain's DNS are setup incorrectly on CloudFlare side and A record points to a different server

Resolution

Contact CloudFlare support for assistance.