Items added to order not showing up?

i’m trying to make a plugin that lets you copy items form one order into another

I do the following:

    $old_order = wc_get_order($old_order_id);
    duplicate_line_items($new_order, $old_order);
    //re-fetch order to make sure changes aren't lost.
    $new_order = $wc_get_order($new_order->get_id());
    $new_order->calculate_totals();
    $new_order->save_meta_data();
    $new_order->save();

My duplicate_line_items function looks like this:

    function duplicate_line_items($source_order, $new_order){
        foreach ($source_order->get_items() as $item){
            $new_order->add_item($item);
        }
        $new_order->apply_changes();
        $new_order->save();
    }

When I run this code, the items do not display in the admin view of the “new” order (the destination order), nor do they show up in the database (select * from wp_woocommerce_order_items WHERE order_id = <destination order post id>).

I do see that per the WC_Order::add_item() docs, “The order item will not persist until save.”, but i am saving the order, several times.

Am I missing a step here or something?

Thanks!