how making a selection from a taxonomy selector fixed definitively

I have created a taxonomy “Ospiti” (guests) and set a selector in order to write the number of guests. If I select the number “7” and then edit the post , I see in the posts admin colum the n “7” correctly in correspondence of that post (apartment), but if I want to edit again that post the selector has lost the selection (I see it on 2 and not on 7). Pic of the selector: https://ibb.co/9wtqcdr

I write here the code I used, someone can fix this error?

// Creazione tassonomia ospiti
add_action( 'init', function() {
    $labels = array(
        'name'              => _x( 'Ospiti', 'taxonomy general name' ),
        'singular_name'     => _x( 'Ospite', 'taxonomy singular name' ),
    );
    register_taxonomy( 'numero_ospiti', array( 'post' ), array(
        'hierarchical'      => false,
        'labels'            => $labels,
'meta_box_cb'       => "post_categories_meta_box",
'show_admin_column'  => true,
 'public'            => true,
        
    ) );
} );

add_action( 'admin_head', function() {
    ?>
    <style type="text/css">
        #newtaxonomy_name_parent {
            display: none;
        }
    </style>
    <?php
});
add_action( 'admin_init', function() {
    if( isset( $_POST['tax_input'] ) && is_array( $_POST['tax_input'] ) ) {
        $new_tax_input = array();
        foreach( $_POST['tax_input'] as $tax => $terms) {
            if( is_array( $terms ) ) {
              $taxonomy = get_taxonomy( $tax );
              if( !$taxonomy->hierarchical ) {
                  $terms = array_map( 'intval', array_filter( $terms ) );
              }
            }
            $new_tax_input[$tax] = $terms;
        }
        $_POST['tax_input'] = $new_tax_input;
    }
});

//creating a META BOX
function custom_meta_box_markup($object)
{
    wp_nonce_field(basename(__FILE__), "meta-box-nonce");
    ?>
    <div>
      
        <label for="meta-box-ospiti">N.ospiti</label>
        <?php
        $selected_terms = wp_get_post_terms($object->ID, 'numero_ospiti', array('fields' => 'ids'));
        $args = array(
            'taxonomy' => 'numero_ospiti',
            'selected' => $selected_terms,
            'name' => 'tax_input[numero_ospiti][]',
            'hide_empty' => false
        );
        wp_dropdown_categories($args);
        ?>
    </div>
    <?php
}

function add_custom_meta_box()
{
     add_meta_box("demo-meta-box", "Ospiti", "custom_meta_box_markup",
"post", "side", "high", null);
}

add_action("add_meta_boxes", "add_custom_meta_box");

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