This is because not all students have accepted your invitation yet.
When you invite a student from your dashboard, s/he will get a notification in the app. Upon accepting the invitation, the student will appear in your dashboard. You can then see how much they are practicing and how it is going with their practice.
If your student needs any help with that, perhaps you can look at his account together next time you see in your lesson.
Alternatively, please feel free to have your students contact us directly by submitting a support request in case they need any help with Yousician any time.