We don't know. Please ask Google. It should be.
Our site should have all the meta tags that Google Scholar uses for indexing. You can see the meta tags when navigating to the article page and then selecting "view source" in your browser. The meta tags need by Google Scholar are documented here: https://scholar.google.ca/intl/en/scholar/inclusion.html#indexing
Please only contact us if the meta tags on our end are faulty or incorrect.