Problem generating the sitemap file using YOAST SEO plugin

MJ theme: Version 8.9.1
YOAST plugin: Version 3.4.1

I have been unable to generate the site map file for my site. I googled around, and found a lot of forums where people are saying the issue is that a blank is being inserted somewhere by either the theme or a plugin. I turned off all the plugins, and still get the error. So there must be something wrong in the theme. I checked the functions.php looking for any spaces and eliminated all I found. Still, the issue persists.
Has anyone had this issue?
https://wordpress.org/support/topic/yoast-seo-xml-sitemap-error

BELOW YOU CAN SEE THE LINK TO THE SITEMAP FILE, and the error.
https://www.chiveando.com/sitemap_index.xml

This page contains the following errors:

error on line 2 at column 6: XML declaration allowed only at the start of the document
Below is a rendering of the page up to the first error.