Symfony form render error`. How to fix this issue?

I've got this error and do know why is this happening. It was working two days ago:

An exception has been thrown during the rendering of a template ("Field "app_config" has already been rendered, save the result of previous render call to a variable and output that instead.").

Thats the view:

{{ form_start(form) }}
    {{ form_widget(form) }}
    <button class="btn btn-outline-success">{{ button_label|default('app.save'|trans) }}</button>
{{ form_end(form) }}

And the controller:

$appConfig = new AppConfig();
        $form = $this->createForm(AppConfigType::class, $appConfig);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            $appConfigRepository->add($appConfig, true);

            return $this->redirectToRoute('backend_settings_index', [], Response::HTTP_SEE_OTHER);
        }

        return $this->renderForm('backend/crud/backend_settings/new.html.twig', [
            'app_config' => $appConfig,
            'form' => $form,
        ]);

The error cames from FromRenderer.php

/**
     * {@inheritdoc}
     */
    public function searchAndRenderBlock(FormView $view, string $blockNameSuffix, array $variables = []): string
    {
        $renderOnlyOnce = 'row' === $blockNameSuffix || 'widget' === $blockNameSuffix;

        if ($renderOnlyOnce && $view->isRendered()) {
            // This is not allowed, because it would result in rendering same IDs multiple times, which is not valid.
            throw new BadMethodCallException(sprintf('Field "%s" has already been rendered, save the result of previous render call to a variable and output that instead.', $view->vars['name']));
        }
``