I Have a form on a page which updates a single field of a Node. The form uses ajax to update the field and returns the newly saved entity and replaces the current HTML so the new field is showing up correctly.

This works fine the first time the form is fired, but breaks after that with the following error in my console:

An AJAX HTTP error occurred

There’s no further error report which would tell me more about this error.

Here is my form code:

<?php

namespace Drupalats_tweaksForm;

use DrupalCoreFormFormBase;
use DrupalCoreFormFormStateInterface;
use DrupalnodeEntityNode;
use DrupalCoreAjaxAjaxResponse;
use DrupalCoreAjaxReplaceCommand;

use SymfonyComponentDependencyInjectionContainerInterface;

/**
 * Onboarding form.
 */
class UpdateApplicationStatusForm extends FormBase {

  /**
   * Form ID.
   *
   * @var string
   */
  protected static $formId;

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    $formId = 'update_application_status_form';
    if (self::$formId) {
      $formId = $formId . '_' . self::$formId;
    }
    return $formId;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    // Instantiates this form class.
    $instance = parent::create($container);
    return $instance;
  }

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $node_id = $form_state->getBuildInfo()['args'][0];

    self::$formId = $node_id;
    $application = Node::load($node_id);

    $field_definitions = Drupal::service('entity_field.manager')->getFieldDefinitions('node', 'application');
    if (isset($field_definitions['field_application_status'])) {
      $status_options = options_allowed_values($field_definitions['field_application_status']->getFieldStorageDefinition());
    }

    $form['#attributes']['id'] = $this->getFormId();

    // Application select list.
    $form['status'] = [
      '#type' => 'select',
      '#title' => $this->t('Sollicitatiestatus'),
      '#options' => $status_options,
      '#default_value' => $application->get('field_application_status')->getValue()[0]['value'],
      '#ajax' => [
        'callback' => [$this, 'submitForm'],
        'wrapper' => 'mapping',
        'effect' => 'fade',
      ],
    ];

    $form['nid'] = [
      '#type' => 'hidden',
      '#default_value' => $node_id,
      '#value' => $node_id,
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $node_id = $form_state->getValues()['nid'];

    $application = Node::load($node_id);

    $application->set('field_application_status', $form_state->getValues()['status']);
    $application->save();

    $view_builder = Drupal::entityTypeManager()->getViewBuilder('node');
    $storage = Drupal::entityTypeManager()->getStorage('node');
    $node = $storage->load($node_id);

    $build = $view_builder->view($node, 'teaser');
    $form_state->setRebuild(TRUE);

    $response = new AjaxResponse();
    $response->addCommand(new ReplaceCommand('#application-' . $node_id, $build));
    return $response;
  }

}