We are having trouble getting a "ContentDocumentLink" object back to a .net client via an authenticated API call. A similar call works fine for records from the "Attachment" object. The credentials used for the same user that uploaded the file. That user is the owner of the file.
Querying for the ContentDocumentLink with "LinkedEntityId = xyz" works successfully from the Developer Console query screen.
What could cause the owner of the ContentDocumentLink to not be able to get it via the API?