I have created a custom taxonomy and the sitemap for that taxonomy appears in my sitemap_index.xml as normal. Whenever I click on the sitemap for my custom taxonomy it goes to my 404 page. This is strange as I have exactly the same taxonomy on another site, and that sitemap works fine.
Then I noticed that when on the term page within the admin, under Include in sitemap?: if I select 'always include' the 404 disappears and I will have 1 term showing on my taxonomy sitemap.
Any ideas why the sitemap is not working without me having to do this every time? I am using the latest version of WordPress SEO (18.104.22.168).