What does HTTP status 208 (Already Reported) mean?

HTTP_STATUS_ALREADY_REPORTED

This status is defined for WebDAV collection bindings. It tells the client that the server already reported the relevant binding earlier in the same depth traversal, preventing repeated enumeration and loops.

It is meaningful only inside a DAV:multistatus response. Clients should retain the earlier result for that resource instead of treating 208 as a general-purpose HTTP success code.

This status is meaningful inside a 207 Multi-Status response and is intended to suppress repeated enumeration of the same WebDAV binding or member. A client should interpret it together with the surrounding multistatus body rather than as a stand-alone success response for an unrelated HTTP request.

RFC 5842: Binding Extensions to WebDAV