5.6.1. wasn’t supposed to fix it as far as I know. In 5.6 the default was set to remove the standard WP custom field meta box display to improve performance of the WP admin. I’m sure that it’s possible to create a WP init action or perhaps on some other WP hook, that can determine what admin page is being loaded and decide if it should be shown or not. or you can add
add_filter('acf/settings/remove_wp_meta_box', '__return_false');
to functions.php to show it everywhere. I’ve personally never had much use for the WP custom field editor. I feel that letting it be displayed is a good way to allow people that don’t know what they are doing to have access to things that they should not be allowed to alter.
