Hello Alvaro,
Thank you for switching to Rank Math.
The first thing you need to do is determine whether you have a blank page or a white page. It sounds all the same but there is a difference. Check the source code of the blank/white page.
https://www.computerhope.com/issues/ch000746.htm?utm_campaign=RankMath
If the source code of the sitemap page is empty, there must be a conflict with another plugin or the theme. You can use the Health Check plugin to determine which plugin or theme is causing this. Another scenario is that you have a static file with the same name as you sitemap file (sitemap_index.xml).
You should FTP into your server and remove the file.
Please check this page for more details on common Sitemap related issues:
https://rankmath.com/kb/check-plugin-conflicts/
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.