The difference in the link is intentional. The regular link (https://www.kerryfung.com/publication/what-is-bodytalk-3/) is a landing page for the publication and is meant to display the publication’s information, along with a pair of links to either open or download the publication.
From what I saw on your site, the problem is that the default landing page template is incompatible with your theme. The landing page template is the file /includes/single-publication.php
and is based on the WordPress default themes.
To customize things, you’d need to drop a copy of single-publication.php
into your theme and modify it to fit the sidebar placement of the rest of the site. Unfortunately, this is a case-by-case customization thing and not something I can predict or prepare for in code.