wp-sitemap.xml is not crawled

[zukilover]

Describe the bug
wp-sitemap.xml is not being crawled by the plugin. sitemap.xml is generated instead.
This caused an issue when we have dynamic robots.txt that points the sitemap to the wp-sitemap.xml

I have done a workaround by uploading a manual robots.txt

Expected behavior
A wp-sitemap.xml should be crawled so that we do not need to manually upload robots.txt