The size guide feature (custom post type) was developed to add a size chart to a product page. This function can be activated in Theme Settings -> Shop and the Size guides option is enabled at the bottom of the setting. A new size guide chart can be added in Dashboard -> Size Guides.
Each product has the option to choose the size guide among all the existing ones. In addition, there is the option to hide the chart and leave the content area allowing to add custom content in the popup window to each product.
If the size guide has been created and assigned to a category but does not appear in the product page, it is necessary to check if it has not been hidden in the product page:
If the Size Guide table is not assigned to any of the categories, it is necessary to choose it from the drop-down in the product page.