The custom fields created using our plugin will show in the Admin area if the option “Display in Order Detail Pages” is enabled.
However, while using the plugin Advanced Custom Fields, they are hiding the display of the custom fields on the order detail page for better performance.
They are also providing a solution on their website. You need to add the below hook in your theme’s functions.php inorder to show the custom fields in the admin area.
add_filter( ‘acf/settings/remove_wp_meta_box’, ‘__return_false’ );
For more details please refer to the below link:
https://www.advancedcustomfields.com/blog/acf-pro-5-5-13-update/
Hope this will help.
Thank you!