Recently had a wordpress side with the following error

Fatal error: Cannot redeclare wp_get_global_styles_custom_css() (previously declared in /data04/xxxx/public_html/wp-includes/global-styles-and-settings.php:254) in /data04/xxxxx/public_html/wp-includes/deprecated.php on line 6323

Issue was the WordPress Autoupdater had issues replacing the files

Recopying the wp-admin and the wp-includes from a fress download of WordPress resolved the issue