Hello,
Thank you for contacting the support and we regret the inconvenience caused.
Please follow the below steps and see if that helps:
1. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/pipRDp
2. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server. For plugins or Cloudflare, please follow this article:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
3. Clear your website and browser’s cache and check the sitemaps again.
Please let us know how that goes.
Thank you.