Error: The entity type does not exist

Problem/Motivation

On a view with relationships it's not possible to apply the filter. If I click on "Apply and continue" I get this error:

"
An AJAX HTTP error occurred.
HTTP Result Code: 500
Debugging information follows.
Path: /en/admin/structure/views/ajax/handler-extra/teilnehmerliste/page_2/filter/eref_node_titles
StatusText: error
ResponseText: The website encountered an unexpected error. Please try again later.Drupal\Component\Plugin\Exception\PluginNotFoundException: The "" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition() (line 150 of core/lib/Drupal/Core/Entity/EntityTypeManager.php). Drupal\Core\Entity\EntityTypeManager->getHandler(NULL, 'storage') (Line: 208)
Drupal\Core\Entity\EntityTypeManager->getStorage(NULL) (Line: 355)
Drupal\entity_reference_exposed_filters\Plugin\views\filter\EREFNodeTitles->generateOptions() (Line: 231)
Drupal\entity_reference_exposed_filters\Plugin\views\filter\EREFNodeTitles->submitExtraOptionsForm(Array, Object) (Line: 107)
Drupal\views_ui\Form\Ajax\ConfigHandlerExtra->submitForm(Array, Object)
call_user_func_array(Array, Array) (Line: 259)
Drupal\views_ui\ViewUI->standardSubmit(Array, Object)
call_user_func_array(Array, Array) (Line: 114)
Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object) (Line: 52)
Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object) (Line: 593)
Drupal\Core\Form\FormBuilder->processForm('views_ui_config_item_extra_form', Array, Object) (Line: 321)
Drupal\Core\Form\FormBuilder->buildForm('Drupal\views_ui\Form\Ajax\ConfigHandlerExtra', Object) (Line: 215)
Drupal\views_ui\Form\Ajax\ViewsFormBase->Drupal\views_ui\Form\Ajax\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 217)
Drupal\views_ui\Form\Ajax\ViewsFormBase->ajaxFormWrapper('Drupal\views_ui\Form\Ajax\ConfigHandlerExtra', Object) (Line: 126)
Drupal\views_ui\Form\Ajax\ViewsFormBase->getForm(Object, 'page_2', 'ajax') (Line: 37)
Drupal\views_ui\Form\Ajax\ConfigHandlerExtra->getForm(Object, 'page_2', 'ajax', 'filter', 'eref_node_titles')
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 50)
Drupal\ban\BanMiddleware->handle(Object, 1, 1) (Line: 91)
Drupal\shield\ShieldMiddleware->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 708)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)
"

The error only appears on this filter. Do you have hint for me?

Steps to reproduce

Unclear... Because on another view on the same project, the filter is working normal. Maybe it's because in the error-view I use also another module to get webform submission values: https://www.drupal.org/project/webform_views →