Steps to replicate the issue:

1. Create a course.
2. Create a forum with grading type set to Point and grading method set to Rubric.
3. Create a rubric with at least 4 criteria and 4 levels.
4. Create 5 topics for the forum.
5. Enrol two student.
6. Log in as student 1 and comment all 5 topics with large comment.
7. Log in as teacher/admin.
8. Access the forum and click Grade users.
9. Select student 1 and scroll down to the bottom of the page.
10. Confirm, that grading panel doesn't display View discussion for the last topic.
11. Confirm, that Yes, send notification to student is also not visible on the right side of the panel.
    
12. Select student 2.
13. Confirm, that No posts is displayed.
14. Confirm, that Yes, send notification to student is visible on the right side of the panel.
    

This seems to be a bit similar to MDL-67697.