Do you happen to have a scored interactive object such as a button or clickbox on that final slide? If so, that object forms part of the Quiz Scope and your Quiz Results page is trying to place itself at the end of the Quiz Scope to correctly show all results.
If your slide does not have any scored objects, just drag the Quiz Results slide in front of it again.
Are you trying to create another Question slide after the result slide?
Or is it a normal slide?