Thank you for contacting the support, and sorry for any inconvenience that might have been caused due to that.
Can you please follow these steps?
1. Flush the Sitemap cache by following this video screencast:
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:
That should fix the issue. Please let us know if that does not work. We are here to assist.