Why do I see x-xdn-caching-status: ok but server-timing: xdn-cache; desc=“MISS”

Why do I see x-xdn-caching-status: ok but server-timing: xdn-cache; desc=“MISS”?

x-xdn-caching-status: ok means that the request is cachable.

This was request was a miss.

Subsequent requests for it should be cache hits.