Hi @pigus!

The Yoast SEO plugin should create a sitemap index if the feature is enabled. However, there are instances where there might be plugin conflicts (where it generates its own sitemap) or other server-level issues that could cause problems.

Have you created a topic on our support forums? If not, please do create a topic and we’ll try to see if we can help you out there. If you have a premium subscription, please feel free to email us directly so we can sort it out. Thanks!