Hi,
The ordering is based on what you select in the "ordering column" of the "products options" tab of your menu item.
The default value "ordering" is based on the ordering of the product in the current category. If you display categories of sub categories in a menu item, then there is no direct link for the ordering of the products in that category.
So I would suggest selecting another column.
You could select "product_name" to have them sorted in alphabetic order.
Or you could create a custom field of the table "product" via the menu Display>custom fields and select that column for the ordering. Then, in each product, you could enter the order of the product in that category.