by Davo Smith.
The old version of my pdf plugin had no way of directly gathering some of the required information to provide the PDF grading links, so had to do extra DB queries for each user in the list to gather this information.
Newer versions of Moodle included API changes to the assign module that allowed this data to be gathered directly, without extra DB queries.
I'm surprised it made that much of a difference, but I'm glad it is now working much better on your site.