One of our teachers fell on this one today. When she tried to rescale her forum's maximum grade, Moodle didn't even show the rescale menu... I was able to reproduce this systematically on Moodle 3.1.2, 3.1.3 and 3.2 DEV.
Follow theses steps :
- Create a forum with ratings.
- As a student, write a post.
- As a teacher, grade the post.
- Go back to the forum's setting and try to rescale the maximum grade.
Result: There will be no rescale menu (yes or no). This makes it impossible to rescale the activity because it will give an error.