Hazel is giving unreliable results

I gave Hazel a very simple rule to tag PDF files with an empty the Author field in their metadata.

It was able find some of them. But, it missed more than half of them.
All of the pdfs are healthy (not corrupted); I am able see and open their author field (Properties) is empty.
Why is it?
It was able find some of them. But, it missed more than half of them.
All of the pdfs are healthy (not corrupted); I am able see and open their author field (Properties) is empty.
Why is it?