I suddenly started getting a 524 error on two subdomains on WordPress Multisite hosted at WPengine. WPengine said it’s not their server and the problem is with CloudFlare. I changed the DNS to send traffic directly to WPengine and the sites were working. I changed back to CloudFlare and I got the 524 error again, so I changed back to WPengine.
I don’t know what to do to use CloudFlare.