We recently upgrade our moodle from 2.7 to 3.1.4+ and we noticed some problems with Range into user report..
Let me explain..
In this screenshot, you can see Range is showing correctly 0 to 925 for all the users and we also have correct grades here..
Now look at this screenshot: the Range for same student is 0 to 260 which is wrong
So you can see for first student, range is correct into Single View BUT it is incorrect into User Report.. And because of wrong range, percentage is also being calculated on wrong range.