The fingerprint filter is the correct way to do that, the point that Stephen talked about is that using the [@metadata][fingerprint] field can interfere in the troubleshooting and debugging since the [@metadata] field is not present in the output.
But as we can see, the id of your document was the literal value [@metadata][fingerprint], this happened because the referecen in the document_id option was wrong, it should use the sprintf format as you can see in my last post.