The feedback comments for assignments is not displayed in the User Report unless the assignment has been given a grade.
If the assignments is given a grade, the comment is visible, even after subsequently removing the grade.
To reproduce:
1. Go to grade assignment for a student.
2. Provide feedback, but no grade.
3. Check User Report for feedback.
4. Give a grade to assignment for the student.
5. Remove the grade.
6. User Report now shows the feedback.