Phantom balls

Hi. I'm an experienced programmer, but I'm new to Unity. I am developing a 2D game style boucing balls. When a ball falls with normal gravity I can see how 2 or 3 balls appear (you can see the attached image) I guess it's a refresh problem between frames. I do not use any script to move the ball, only Unity physics. I was looking for and reading several articles, I tried to modify parameters in the editor ... but I can not get that problem solved. Is it something that should be done by script? Is it some parameter in the editor? Any help I will thank you. Best regards.