This happens to us as well.
We go to a student's individual grading screen and assign some feedback (before the student ever attempts the assignment), and then click Save, this feedback does NOT show up in the user report.
HOWEVER, once back at the view/grade all screen and you click "Save all Quick Grading Changes" (even though we did not enter the feedback on the quick grading screen), this pushes that feedback to the user report. This method works consistently for us on 2.8 and 3.0.