This is actually not an issue. While you are creating a single product template it doesn’t contain any actual product data. That’s why some of the widgets appear blank on the Elementor editor page. These widgets – product price, product rating, product comparison button, additional information, product stock, product meta, and product data tabs will only show the logo in Elementor editor.
You can keep an actual single product of your site open on another tab of your browser and refresh it while you are making the changes on the single product template. Also, make sure that the template is set for the product you are viewing on another tab. You can also set the template for all the products. Otherwise, the product you are viewing will not reflect the changes you are making on the template.