This was an issue that was previously reported in MDL-31036

Replication Steps:
1. Go to qa.moodledemo.net
2. Log in as an instructor
3. Create an assignment activity
4. Log in as a student and make a submission
5. Log back in as an instructor
6. Go to Course -> Grading
7. Go to Single View
8. Select the user that submitted to the assignment
9.Leave feedback with a less than symbol or some HTML

10. Save the feedback
11. Look at the User Report for that user

Expected result
    All feedback is visible

Actual Result

    Everything after "<" is removed, in the case where there are paired "<" and ">" everything after the ">" remains so this is clearly broken HTML sanatisation.   

NOTE:  The output is also broken in the Grader report also