Sharing a collection with students and sending an activity are two different things.
When you share a collection with your students, sharing does not mean sending the activities contained in the collection.
These activities will not appear in the Track Assignments Report but rather in the Collections Report.
The collections shared with your students will be prominently displayed on their homepage in the My Library section.
Activities that are sent will appear in your Track Assignments Report. For your students, they will appear in the Training Zone section of their homepage.