Not possible to determine the problem from your animation. What you really need is the Tool Options dock open. Then you can see the aspect ratio setting. That needs to be 1:1 Do not assume that Current is 1:1 A previous selection can set some other value.
A quick demo of that situation, followed by a 1:1 selection. https://i.imgur.com/AZfOmqR.mp4
A quick demo of that situation, followed by a 1:1 selection. https://i.imgur.com/AZfOmqR.mp4