Comment by svachalek

4xx errors are for when the client did something wrong and needs to know about it. 5xx errors are for when the server is having problems and the only people who can do anything about it are the operators, who should be looking for errors in the logs rather than the HTTP client.

Truly "application level" issues are therefore correct as 200, although some application communication issues lead to 4xx errors that should be handled as such. But the case of an application trying to communicate via 5xx errors should never have been the case anyway.