Plugin ignore my weight modifications

Good evening.
Due to my client needs, I had to write some code to change the weight of my cart, to be able to apply some charge on shipping fees in case my cart contains specific items.

I wrote a function that makes all the calculations, and returns the new weight of the cart.

function set_my_weight($weight) {
  global $woocommerce;
  $cart_items = $woocommerce->cart->get_cart();

  // all the magic here (a lot of code... not interesting now)

  return $weight;
}
add_filter('woocommerce_cart_contents_weight', 'set_my_weight',10,1);

Your plugin seems not to look a the cart weight. It seems to calculate the total weight article by article, instead. That’s a real problem to me.

Is there a way to force your plugin to get the correct value by a WooCommerce function?

Thanks