It is a known limitation that Content Library Service does not synchronize empty library items.
An empty library item should not result if vSphere Web Client is used to import a library item. An empty library item comes up when using the Content Library API, because importing an item to a content library involves multiple steps. First, create a library item, which will initially have no content. Then, upload files to the library item using the UpdateSession class.If content is not uploaded to the library item, it remains empty.