Das Problem (Logs überfüllt mit):
Notice: Trying to access array offset on value of type null in Drupal\views\Plugin\views\display\EntityReference->query() (Zeile 195 in /var/www/web/core/modules/views/src/Plugin/views/display/EntityReference.php)
core\modules\views\src\Plugin\views\display\EntityReference.php (Line 156):
// $options = $this->getOption('entity_reference_options');
$options = $this->getOption('entity_reference_options') ?? [];