Yann, thanks for the fix.
And yeah, that was a pretty face-palm error, haha.
About the cell size error, so many globals and different numbers everywhere (I'm trying to keep track of all this in my head), sometimes I forget to update something!
I did the formula for placing startsprite and endsprite very late at night, but now I see what you mean.
And yeah, I figured I was creating an infinite loop when I saw nothing but gray on my screen ;)