404 Page for subsites in WP Multisite

Problem was resolved for me, but I was using custom post types. For others using cpt’s, be sure to add support this way in functions.php:

add_action('init', 'my_custom_init');
function my_custom_init() {
    add_post_type_support( 'my-cpt', 'front-end-editor' );
}

Replace my-cpt with the slug of your custom post type.