Conflicting information on a sitemap

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Natalie Coyne: Can you walk me through why you would want the sitemap deindexed ?
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  Nathan Nikolay Gaidy: Google Search Console Coverage report gave me an error report that the sitemap.xml is not indexed. It is not my website.
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  Natalie Coyne: Check your robots.txt to see if it is noindex-Ed and then remove it.
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  Nathan Nikolay Gaidy: Natalie Coyne
  Disallow: /wp-admin/
  Allow: /wp-admin/admin-ajax.php
  
  Sitemap: https://*************.com/sitemap.xml
• 
  Nathan Nikolay Gaidy: That is all there is
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  Michael Martinez: I know of no reason to manage indexing for XML sitemap files. If you don`t want Google to find the files then delete them or block them via "robots.txt".
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  Nathan Nikolay Gaidy: Good morning Michael!
  My question basically is should the sitemap be indexed and if not why is Google sending me a coverage report error for it not being indexed?
• 
  Michael Martinez: Nathan Nikolay Gaidy I would not try to block it from being indexed in any way. But if you`re not trying to do that and Google is reporting the error, then I would look for a technical issue on the server. Check your error log files to see if something is wrong when Google tries to fetch the XML sitemap.
  
  You could try fetching it with the Mobile-friendly Testing tool to see if that produces an error.
  
  ON EDIT: I just saw your other reply. I would not mark a sitemap with "noindex".
  
  https://search.google.com/test/mobile-friendly
• 
  Nathan Nikolay Gaidy: http://www.alanhart.co.uk/.../wordpress-xml-sitemap.../
  
  So basically the html sitemap is set as no index and google does not seem to like it :D