Hello,
Please follow these steps to flush your sitemap cache:
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. Disable the transient cache for the sitemap by applying this filter. This will make sure that your XML sitemap always reflects the latest changes on your site:
/**
* Filter if XML sitemap transient cache is enabled.
*
* @param boolean $unsigned Enable cache or not, defaults to true
*/
add_filter( 'rank_math/sitemap/enable_caching', '__return_false');
If you’re not sure how to add this code, you can follow this guide:
https://rankmath.com/kb/wordpress-hooks-actions-filters/
If the issue persists, we might need to take a closer look at the settings. Please edit the first post on this ticket and include your WordPress & FTP logins in the designated Sensitive Data section.
Please do take a complete backup of your website before sharing the information with us.

It is completely secure and only our support staff has access to that section. If you want, you can use the below plugin to generate a temporary login URL to your website and share that with us instead:
https://wordpress.org/plugins/temporary-login-without-password/
You can use the above plugin in conjunction with the WP Security Audit Log to monitor what changes our staff might make on your website (if any):
https://wordpress.org/plugins/wp-security-audit-log/
We really look forward to helping you.