Two attachement URLs in XML sitemap

Hi, I′ve had issues with the attachements shown as content pages in Google. So I′ve updated Yoast to the last version released yesterday and installed Search Index Purge Plugin.
I checked the sitemap generated by Yoast and it has two URLs with attachements, last week it doesn′t show any URLs for attachements, it had just 3 URLS (it was wrong) but is it normal that nowadays my XML Sitemap Index file contains 2 sitemaps of attachements? They had 80 urls each one, the same URLs. Some of them are grey because they are not existing pages (404 errors).
I don′t know if the 2 attachement sitemaps are a correction of the previous error, or if they are a current error, I′m afraid of duplicated content.
Could you help me? thanks!