Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
This error normally comes up when another plugin or a theme modifies the sitemap but since you have already tested for conflicts, it is likely that there is some whitespace on your sitemap index arising from an empty space on your functions.php file.
You can quickly test if this is the case by switching to one of the stock WP themes and check if you can reproduce this issue.
Looking forward to helping 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.
