Every time I update a product, its content template is removed from it. I then have to manually link/connect the template again ( /wp-admin/admin.php?page=view-templates&arrangeby=usage&usage=single )
It seems what is happening here is that you've set the content template to be applied to the entire post type rather than just 1 single post.
You will need to go to your content template and edit it and then uncheck the post type that is selected. Once you've done this update your content template and try creating another product and let me know if the issue still remains.