Animation doesn´t appears correctly on canvas

I don´t know if this is the right place to post this or maybe it should be directly on GitHub (If not, please my apologies) … Well, what happens is that I’m starting with the Step by Step Manual ( and in the first practice I have a strange behavior when playing the animation on the canvas own.

This is the first animation of the manual where a circle moves to right and returns to the left. Well, when the animation reaches the end (2s) the animation sometimes does not reach your site. This occurs under Windows and Linux and on two different computers.

I uploaded a video on YouTube to better illustrate it:

Please, my apologies if this is not the right place to post, please let me know, thanks … greetings!