This is caused by your server or host provider’s network.
Error 524 error indicates that Cloudflare made a successful TCP connection to the origin web server, but the origin did not reply with an HTTP response before the connection timed out.
Typically, Cloudflare waits 100 seconds for an HTTP response. If the origin doesn’t respond in that time, Cloudflare closes the connection and serves Error 524.
Full article including troubleshooting tips:
https://support.cloudflare.com/hc/en-us/articles/200171926-Error-524-A-timeout-occurred