Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
Are you adding the sitemap_index.xml sitemap? You don’t need to add any other. Also, could you share (in the Sensitive Data section) the website URL so we can check it and try to figure out the cause of your issue?
Could you get in touch with your server provider and check with them if they haVe any cache mechanism in place. If there’s none, please remove your sitemaps and resubmit your sitemap in GSC. Let us know how it goes.