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.
Could you please share the affected sitemap URL so we can check as well? You can add it to the sensitive data section

It is completely secure, and only our support staff has access to that section.
Meanwhile, please make sure that your sitemap is not getting cached. Please follow these steps:
1. Ensure you’re using the latest version of your plugins/theme including the Rank Math plugin.
2. Flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/xXXhDt
3. Exclude the Sitemap files of the Rank Math plugin in your caching plugin. The cache could be via a plugin or from the server:
https://rankmath.com/kb/exclude-sitemaps-from-caching/
Once done, remove all your submitted sitemaps and resubmit your main sitemap only. Then, give Google some time to recrawl your site.
Let us know how this goes.
Thank you.
Hello,
I have updated the sensitive data as requested. Can you please check further?
Thank you.
Also. did all the updates you mention above. I decrease the number of post pages to 400 from 900. THen it cause this error. https://ibb.co/ftkLPKM
Hello,
We apologize for the delay in response.
I checked your sitemap page and is loading just fine, however, all of your 4 sitemap URL variations don’t redirect to a final variation as you can see in my screenshot below:

Please follow this guide and redirect to a final variation:
https://rankmath.com/kb/couldnt-fetch-error-google-search-console/#num-5-4-redirect-all-three-other-versions-to-your-preferred-variation
Once done, clear your website cache and try submitting your sitemap to your Google Search Console again. See if this resolves the issue.
We are looking forward to hearing an update from you. Thank you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.