ok found the solution !
I started my iframe code with :
var WIDTH = window.innerWidth;
var HEIGHT = window.innerHeight;
because of a resize function when the iframe is resized
I replace these 2 lines by
var WIDTH = 680;
var HEIGHT = 905;
i commented var winResize = new THREEx.WindowResize(renderer, camera);
and now it's working.
Even without the code that set the scrolling to "no"
so I guess I won't be able to make a responsive app or website like this, but I can definitvely make an iPad version with a different location. I will see later
Anyway thanks for the help