Issue Smart Update for Wordpress - 'Malformed sitemap given'

[TriJoe]

Smart Update test run could not be performed due to errors. Address the errors and try running Smart Update again.

• Malformed sitemap given

We're unable to get the website to update using Smart Update. We're using Yoast SEO plugin which generates the sitemap at https://site.com/sitemap_index.xml.

Can someone shed some light in to how Smart Update obtains the XML file, and if there are logs to see the actual issue? Smart Update works on all of our other sites.

 

[TriJoe]

I disabled Yoast SEO XML and used another Sitemap tool which is working.