Actually, you certainly can have a different outcome each time you press the button.
This is because the estimator has to guess what will happen.
Especially if you are asking it at a time when it is totally uncertain - when the borders are nowhere near clear.
The less certain the outcome, the more different the answer will be each time you press the button.
The analysis tool for score estimation should be used by pressing the button and looking at what it is scoring, then deciding how much of that you believe. It shows you on the board what it thinks each player might get, so it is your job to see if it is guessing right.