Yoast Sitemap is errored when using Generatepress theme

Hello

Suddenly my sitemap is not working. I get

This page contains the following errors
error at line 2 column 6: XML declaration allowed only at start of declaration

After investigating this occurs because of conflict with theme or plugin that adds white or line to the beginning of the sitemap.xml file. When I go to where the file should reside and view page source, I see the first line of the sitemap.xml file is blank thus causing the error.

I loaded the health check plugin to debug. It requires a default theme to be loaded to test each plugin to see when the sitemap.xml fails. I reloaded all plugins successfully with the sitemap.xml file functioning. I then loaded GP premium plugin but it requires the generatepress theme. As soon as both generatepress and GP were loaded the sitemap.xml errored out again.

I've spent quite a few hours researching and testing but I stuck at this point with no idea how to resolve it.

Can you assist?

Thanks. Martha