524 A Timeout Occurred
Meaning
A Cloudflare-specific status indicating that a successful connection was made to the origin server, but the origin did not produce a response in time. It's a variation of a timeout where the TCP connection succeeded but the HTTP response did not complete in time.
When to Use
When the origin server is partially reachable (the connection is established) but the server is too slow to respond fully. Cloudflare uses 524 to differentiate this scenario from a lower-level network timeout (522).
Example
Cloudflare might show a 524 A Timeout Occurred if it connected to an origin and sent the request, but the origin took longer than Cloudflare's maximum waiting time to send back a response (perhaps due to a long-running process or hang).
When Not to Use
Do not confuse with 522; 524 implies the handshake was okay but the server didn't respond in time. As an origin server, you wouldn’t send this. As a proxy developer, you might stick to 504 for all timeouts, but Cloudflare splits them. Outside Cloudflare, 524 is not used.
Source
Unofficial (Cloudflare)