Finally I brought the cab at home to take pictures and it turns out that in fact there was just a problem of loose contact !
The kids could play with a few minutes but when I lift the screen game froze and no longer wanted to leave. Anyway, this is a minor problem, and then children want me to fix it in order to play with
(they liked the simplicity of the game) .
So sorry but for now I keep the cab.
A picture of the screen with the actual bug :
