Strange problems with ajax in a custom views filter plugin

I'm not sure if this is a bug or I'm just doing something wrong so I've tagged it as support for now.

I'm trying to make a custom views filter plugin that uses ajax in the form. It's a multi-vocabulary term select - the user selects a vocabulary then selects a term from that vocabulary from an ajax-populated list.

However, I'm encountering several bizarre issues while trying to set it up. If I provide the ajax callback as [$this, 'updateTerms'] it gives me this ajax error in preview:

A fatal error occurred: Recursion detected

Ajax never even runs in the full view. In this case the widget is not rendered at all and the error occurs even on the first load of the widget.

If I provide the ajax callback as either '::updateTerms' or 'Drupal\de_vocabulary_level_views_filter\Plugin\views\filter::updateTerms' it gives me this error in the views preview:

A fatal error occurred: The specified #ajax callback is empty or not callable.

and, inexplicably, this error on the full view:

An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (8 MB) that this server supports.

This issue occurs even on a fresh minimal install of Drupal 8 core with no extra modules or configuration besides enabling taxonomy, views, views_ui and the custom module itself and adding the filter to a view.

The form is pretty simple and works outside of views.

The form is provided in the valueForm function (though I've had the same results inside buildExposedForm) which is overridden like so:

  /**
   * {@inheritdoc}
   */
  protected function valueForm(&$form, FormStateInterface $form_state) {
    $vocabularies = $this->vocabularyStorage->loadMultiple();
    $vocab_options = array();

    foreach ($vocabularies as $voc) {
      $vocab_options[$voc->id()] = $voc->label();
    }

    $form['value'] = [
      'vocab' => [
        '#title' => $this->t('Vocabulary'),
        '#type' => 'select',
        '#options' => $vocab_options,
        '#empty_option' => $this->t('- Any -'),
        '#empty_value' => NULL,
        '#default_value' => !empty($form_state->get('vocab')) ? $form_state->get('vocab') : NULL,
        '#ajax' => [
          'event' => 'change',
          'callback' => 'Drupal\de_vocabulary_level_views_filter\Plugin\views\filter::updateTerms',
          'wrapper' => 'de-vocabulary-level-views-filter-terms-wrapper'
        ],
      ],
      'de_vocabulary_level_views_filter' => [
        '#title' => $this->t('Term'),
        '#type' => 'select',
        '#empty_option' => $this->t('- Any -'),
        '#empty_value' => NULL,
        '#default_value' => !empty($form_state->get('term')) ? $form_state->get('term') : NULL,
      ],
      '#prefix' => '<div id="de-vocabulary-level-views-filter-terms-wrapper">',
      '#suffix' => '</div>',
    ];

    if (!empty($form_state->getValue('vocab'))) {
      $term_query = $this->entityQuery->get('taxonomy_term')
        ->condition('status', 1)
        ->condition('vid', $form_state->getValue('vocab'));
      $term_query_result = $term_query->execute();
      $terms = $this->termStorage->loadMultiple($term_query_result);
      $term_options = [];
      foreach ($terms as $term) {
        $term_options[$term->id()] = $term->label();
      }
      $form['value']['de_vocabulary_level_views_filter']['#options'] = $term_options;
    }
  }

There's a small ajax callback:

  public function updateTerms(&$form, FormStateInterface $form_state) {
    return $form[$this->options['expose']['identifier']];
  }

Currently it reloads a section of the form from the base of the filter form but the same results occur treating it as if it was just the bit from valueForm.