Hello @shmellycat
Thank you very much for your reply.
I contacted my host per your recommendation. Their response was that sitemap.xml should NOT be indexed and the header is tagged correctly. I post the response below. If they are wrong, let me know. It does make sense to me:
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What happens with your website SiteMap is actually normal and recommended by Google. The website SiteMap should not be indexed by any search engine, this is why most of the SEO plugins will add a noindex tag for the .XML file. You don’t want to remove that header. It prevents the XML sitemap itself from appearing in search results, it doesn’t prevent the URLs listed in it from getting indexed.
If you don’t put a noindex in, the Sitemap itself could appear in search results. It isn’t meant for users to see, and users get really confused if they actually click on it. See Prevent XML sitemaps from showing up in Google search results
Not sure why the plugin developers told you to contact the hosting company for such a situation instead of offering you guidance and explaining to you that this is actually normal for your Sitemap if you want your website to be healthy SEO-wise.
Let me know if you have any further questions or concerns!`