Clear needs_processing transient when adding a product to an order

includes/abstracts/abstract-wc-order.php

@@ -1182,6 +1182,7 @@ abstract class WC_Abstract_Order extends WC_Abstract_Legacy_Order {
 		$item->save();
 		$this->add_item( $item );
 		wc_do_deprecated_action( 'woocommerce_order_add_product', array( $this->get_id(), $item->get_id(), $product, $qty, $args ), '3.0', 'woocommerce_new_order_item action instead' );
+		delete_transient( 'wc_order_' . $this->get_id() . '_needs_processing' );
 		return $item->get_id();
 	}