How to remove a URL from my XML sitemap?
This could either happen because it's node/add/article is included within a menu that's indexed by XML Sitemap or a custom path that was added. 

In either case, a drush command can update the path flag for exclusion &amp; rebuild the sitemap so that it's no longer there.

drush sqlq "UPDATE xmlsitemap SET status = 0 WHERE loc = 'node/add/article'"
drush xmlsitemap-rebuild


If you need to do this through the UI, you'll need to check either /admin/config/search/xmlsitemap/custom for a custom link or edit the menu item that contains it (/admin/structure/menu).