When a Canvas course is concluded at the end of the term, Canvas removes some of the pathways for accessing student file submissions. Student submissions are still available, they're just a bit harder to find. 

1. Navigate to the course. See Where are my old Courses? for help finding it. 
2. Select Assignments from the course navigation menu, and select the assignment.
3. On the right side of the page, click the Download Submissions link to download all submissions for this assignments. Click SpeedGrader to view individual submissions, which you can download one at a time.