by Emma Richardson.
Yes, this has something to do with the enrollments. You mentioned that you reenrolled students in the class - I am wondering if this is a date issue. If you enrolled the students after the date of the assignment, then maybe their activities are not being included in the gradebook because they were not enrolled at the date of the activity. You might also check the start date of the course and make sure that is starts before the activity.
Can you restore the course but restore the users with the course instead of reenrolling them after and see if that doesn't fix the issue?