Sitemap.xml missing for root site under WordPress Multisite

I installed the Infinite SEO plugin this morning and have been experimenting with it. The install went smoothly and I quickly had sitemap generation in place. The sitemaps for my subsites are working fine, but the sitemap for my root site is not working properly. For example these work:

This does not:

In the dashboard it shows that the sitemap was created for the root site and it contains a few items (see screen shot), but the file is not actually present. Do you have any idea what could cause this?

Thank you,