To keep the aspect ratio of a shape, you can come to its Properties pane > Position & Size tab > click the Link width to height checkbox (the chain icon).
To create the circle animation above, you can try following these steps:
Insert an oval shape
In its Properties pane > Styles tab > set No Fill and Solid line style
In the Draw Mode drop-down list > select Partly > type any value in the Line Length box.
For example:
Thanks for reporting the problem.
The cause may be a conflict with canvas snapping when you resize.
You can temporarily fix it by accessing the View menu > click Canvas Snapping to turn it off.