Share your ajax call file (entire js file) so i can help you.

@ShyamHajare - check if anything missing in checkout_cart_product_add_after event function, because above mentioned error is mostly occurred on save of item into quote. :)

go to magento.stackexchange.com/questions/142023/… link for solution.

ok, so try below code $objectManager = Magento\Framework\App\ObjectManager::getInstance(); $_product = $objectManager->create('Magento\Catalog\Model\Product')->loa‌​‌​d($product_id); $_product->getResource()->getAttribute('vendor')->setStoreId‌​(0)->getFrontend()->‌​getValue($_product);