public function resetCart()
    {
        // 全カートアイテム取得
        $CartItems = $this->cartItemRepository->findAll();
        foreach ($CartItems as $CartItem) {
            $xxx = $CartItem->getProductClass()->getProduct()->getXXX();

            // xxxがないアイテムを削除
            if (empty($xxx)) {
                $Cart = $CartItem->getCart();
                $this->entityManager->remove($Cart);
                $this->entityManager->flush($Cart);
            }
        }
    }

Entity has to be managed or scheduled for removal for single computation Proxies\__CG__\Eccube\Entity\Cart@00000000192f4c2a000000006d079031