Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
The sitemap shows a html error if your sitemap loads a 404 page or redirects to homepage. This is pretty common with when caching is enabled on the site. To resolve this, please head to your caching plugin and exclude all your sitemap URLs from being cached then do the following:
1. Head over to WordPress Dashboard > Settings > Permalinks
Hit the save button once.
2. Go to WordPress Dashboard > Rank Math > Sitemap Settings
Hit the save button once.
That should fix the issue.
You can test your sitemap URLs here: https://www.xml-sitemaps.com/validate-xml-sitemap.html
If the issue persists, please do let us know so we can look at this further.
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.