Thanks Luca for your comments.
As I commented in MDL-71252, the checkboxes on the course page are easy for students to miss, especially when the page contains labels with text and images, activity descriptions, restrict access information etc.
I think a better solution for students to be able to see which activities they have completed and still need to complete would be a progress bar or similar. Hopefully this can be included in Moodle 4.0.