598 Network Read Timeout Error
Meaning
A non-standard status code used by some proxies (notably some Microsoft HTTP proxies or services like Amazon CloudFront) to indicate that a network read timed out. This typically means the proxy was reading from an upstream server and timed out.
When to Use
When a proxy or intermediate server times out while reading data from the upstream server, and chooses to signal that with a specific status code to the client (instead of the generic 504). 598 is a network read timeout behind the proxy.
Example
A client might receive a 598 Network Read Timeout from a proxy if the proxy connected to an origin, started reading a response, but the read hung or took too long mid-way. The proxy aborts and returns 598 to indicate this lower-level timeout event.
When Not to Use
Do not use in a standard server context. This is an informal convention for certain network infrastructure. Most systems would just use 504 for any timeout. 598 is rarely seen except in specific proxy or load balancer implementations that distinguish read vs connect timeouts.
Source
Unofficial (HTTP proxy)