Update meta data on export

Hi,
I was trying to create/update metadata field on export job.
I re-used the code changing the order status

add_action('woe_order_exported', function ($order_id) {
    $order = new WC_Order($order_id);
    $order->update_status('completed', 'Exported !');
} );

and replace the 3r line code by :
$order->update_meta_data('_test_field', 'test working');

but doesn’t seem to work (there is no error though).
Did one of your customer already have this issue?

Thank you.