Hello José, how are you?
According to the person who created the interaction, we did not use an exercise slide, because we needed the student to see the answer that was given when advancing the screen and returning to it (just like it works on the conventional exercise slide). However, if the student returned to the course's home screen and clicked again to return to the question, it would have to restart from scratch, which according to my knowledge with an exercise slide, this behavior would not be possible.
In short, the student clicks on the "Les attendus d'un déplacement..." button, and goes to the next screen. The exercise screen.
On the exercise screen, the student positions the items and the validate button appears. When clicking on the button, the student will check whether his answer is correct or incorrect, and then move on.
When advancing, if he goes back, he returns to the exercise screen, but with the correction layer exposed. If you go back one more screen, you will return to the home screen.
When you click on "Les attendus d'un déplacement..." again, the student will go to the exercise screen, but with the screen reset from scratch.
About the elements that overlap one above the other, there is no specific element, sometimes it is one, sometimes it is another.
I was unable to attach the video, but here is the link to download it. In the video, between 1:05min and 1:15min, you will be able to see more clearly the error/bug that occurs.
Video