Fatal error: Uncaught Error: Interface "TYPO3\CMS\Core\SingletonInterface" not found in /var/www/html/dev.hallescherfc.de/vendor/typo3/cms-scheduler/Classes/Scheduler.php:35 Stack trace: #0 {main} thrown in /var/www/html/dev.hallescherfc.de/vendor/typo3/cms-scheduler/Classes/Scheduler.php on line 35