Why is a previously completed course for my learner missing when I run a report?

In order for courses to appear on the report, they need to be turned on and assigned to the user profile. If you no longer want the user to have access to a particular title, make sure you run a report before you turn it off. 

You can re-assign the course and the data will return, it is hidden from the report. 

This often can happen if you have moved a user to a different group, or if you have run a special campaign for a title and then turned the course off.