The addons are not shown on the single product page
This problem may be due to a custom WooCommerce template used by the theme or to the use of a visual composer. If you use a visual composer that allows the customization of product templates, try to use this shortcode to show the add-ons section:
[yith_wapo_show_options]
You can check if it comes from the theme by temporarily replacing it with a default one and check if this solves the problem.