Thank you for contacting the support, and sorry for any inconvenience that might have been caused due to that.
It looks like your sitemaps returned 404 when Google tries to access them. Can you please check your sitemap page and see if it loads correctly? Your sitemap URL should come like this: https://example.com/sitemap_index.xml.
If your sitemap page does return 404, please follow these steps:
1. Flush the Sitemap cache by following this video screencast: https://i.rankmath.com/pipRDp
Thanks, now there is no more 404 error, but in search console nothing has changed. Shall I submit the sitemaps again?
Also I notice that I have to sitemaps for posts. Is that because each site maps contains a max of 200 URL and I have more than 200 posts?