Symfony 3.4 - 刷新页面时会话丢失

I have one problem that I can't explain with my session manager. Well i built a very simple cart. It's create a key in the Symfony Session called "product_cart".

WhenIi come at the "cart page" for the first time, I see my products. But if I refresh the page, the session is empty...

There my cart action page

/**
 * @Route("/{_locale}/submissions/cart", name="frontend_domilia_submissions_cart")
 */
public function indexAction(Session $session) {

    return $this->render(':Frontend/Submissions:cart.html.twig', [
        'products' => $session->get('product_cart'),
    ]);
}

/**
 * @param Product $product
 */
public function addProductToBasket(Product $product) {
    $basketProduct = new BasketProduct();
    $basketProduct->setId(uniqid());
    $basketProduct->setProductId($product->getId());
    $basketProduct->setTitle($product->getTitle());
    $basketProduct->setImagePath($product->getImageMain());
    $basketProduct->setQty(1);

    $productList = $this->session->get('product_cart');

    if (is_null($productList)) {
        $this->session->set('product_cart', [$basketProduct]);
    } else {
        array_push($productList, $basketProduct);
        $this->session->set('product_cart', $productList);
    }
}

I think something break my session but I don't know what, it's a little bit strange...

This happened only in dev mode.

Somebody could help me please? Regards, Christophe