Hi @monbauza,
I spent 3+ days with googling, checking found info and methods described eg. there:
https://kb.yoast.com/kb/my-sitemap-is-blank-what-s-wrong/
I repeat myself, cutting from the code quoted in original support post:
<loc>https://www.mydomain.com/page-sitemap.xml</loc>
contains reference to subdomain “www”
while another part:
href=”//static.mydomain.com/plugins/wordpress-seo/css/main-sitemap.xsl”?>
contains reference to subdomain “static”.
Is it really what you think should be generated?
Don’t xou think <loc> line should also use “static” subdomain in URL?
I also repeat: for site speed reasons I use www as cookie domain and static as cookieless subdomain, for serving images, css and javascript from wp-content directrory.
Maybe something requires cookie for correct sitemap index generation?
No public info about it…