The only purpose of this plugin is to generate a sitemap.
We deliberately break the sitemap down in to smaller pages as per the google sitemap protocol to improve performance. This does not impact the overall function of the sitemap.
XML sitemaps are merely a suggestion to google and other search engines, there are no guarantees that your pages will be listed.
A sitemap is just one small part of your overall SEO strategy, it is not a silver bullet.