This is common with units requiring refresher training (or re-assessment) such as First Aid and CPR units. 

While we're on this topic, PowerPro has a built-in report 'Reports' > 'Client Reports' > 'Refresher List' listing all students who are due for a refresher:

 

For the Refresher List Report to work, please ensure the relevant units and modules have the requalification period set as per example below: