Hello,
Thank you for contacting Rank Math and bringing your concern to our attention. I’m sorry for any inconvenience this issue may have caused you.
Please share your sitemap URL so we can check and validate it as well.
Meanwhile, 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/
Then remove all your submitted sitemaps and resubmit your main sitemap only /sitemap_index.xml
Once done, give Google some time to recrawl your site and wait for the “Last read” date column to be updated as well.
Looking forward to helping you.