Thanks Kirk for your suggestion regarding filters. I checked. They were not the culprit. It must be a misunderstanding of the program functionality on my part. Indeed, after trying to create populated contact sheets, I was finally able to get one populated. In order to do so, I had to select a folder containing images.
I have my images stored on my PC in a 'year' folder which holds 'dates' subfolders. If I select a 'year' folder, my contact sheet will be empty. If I select a 'date' subfolder, my contact sheet will be populated. Is this normal behavior?