I saw that after sitemap is generated, lacks conclusion   </urlset>      I'm wodering why?

I've faced the same problem
which I identified its cause in the timeout in SEO plugin increase it so it can finish creating the sitemap of all your items
or add it manually

Hope it helps

@crymatisticos
That is correct, your hosting break script before it has finished.
On Monday we will release new version of plugin that should generate sitemap much faster