I get this :
error X3084: "numthreads(X, Y, Z)" attribute expected, where "X, Y, Z" are the dimensions of the thread group.
And yes, i've been turning around so much the shader's code that i simply forgot what i started with. After checking every single variable in several cbuffers i've noticed that only those with custom struct was unable to map correctly.
Btw : Thank you for your concern. I've been stuck on this for days.