callback is not invoked

On the online site suddenly the callBacks are no longer invoked. I made a copy of the site on XAMPP (local) and everything works normally.
To understand what could have happened, I created a new content type with a numeric field and activated the callBack which only displays a string via the alert function, but it doesn't work.
It is as if the callback functions are invoked but not executed throughout the site. But in the local everything works normally. This all happened after I upgraded the core from version 8.9.17 to version 8.9.18

Is there a way to check why it doesn't callback?
Below is the code of the field and the callback

field in form_alter

$form['field_importo_contenuto_1']['widget'][0]['value']['#size'] = 12;
$form['field_importo_contenuto_1']['widget'][0]['value']['#ajax'] = [
    'event'           => 'blur',
    'disable-refocus' => TRUE,
    'callback'        => 'cb_aaaa',
 ];

callBack

function cb_aaaa ( array &$form,  FormStateInterface $form_state ) {
        $response = new AjaxResponse();
          $response->addCommand( new AlertCommand( 'OK' ) );
        return $response;
}