Prevent clubbing of server side error messages on top
You can disable that module to return to the more traditional line-by-line error output globally, or hook into it programatically form-by-form:

function MODULE_form_alter(&amp;$form, FormStateInterface $form_state, $form_id) {
  if ($form_id == 'foo_form') {
    $form['#disable_inline_form_errors'] = TRUE;
  }
}