Hi there !
Still have an issue with domain mapping. Indeed, the sitemap URL does NOT take the mapped domain url but remain with the subdomain url on a multisite.
Since i had to manually redefine the site url with the mapped domain since the issue with WPML is not yet solved, consequently the subdomain url does not exist anymore.
Problem : the sitemap url remain the subdomain one so... no sitemap.
The fact is I SEO does not care about domain mapping OR multidomains OR manual domain site change...
In fact the sitemap works with the proper mapped domain URL. Only the mentioned url in Sitemap setting is incorect