Sitemap not found, Multisite with Domain Mapping

I’ve network-activated the WPMU DEV SEO plugin, but the sitemaps are not found.

I am running a multisite network with domain mapping, both plugins from WPMUDEV.

When I go to, it says that the sitemap is not found.

But when I enter the full path to the sitemap file, I found that sitemap files are indeed created in the sub-sites files folder, ie$site_id/files/

Can I know if there are any specific instructions to use this plugin? e.g. htaccess entries, file permissions, plugin configurations etc?