Strange problem with backup und delete

Hi all

We have a big problem, if we try delete a course comes: (Here is the debug warning). A similar warning when we want clone or copy a course. Moodle ist 3.11.3. Any help is welcome!

Greets Andy

error/setting_invalid_ui_label

Weitere Informationen über diesen Fehler
Debug-Info:
Error code: setting_invalid_ui_label
$a contents:
Stack trace:

    line 153 of /backup/util/ui/backup_ui_setting.class.php: base_setting_ui_exception thrown
    line 156 of /backup/moodle2/backup_section_task.class.php: call to base_setting_ui->set_label()
    line 153 of /backup/util/plan/base_task.class.php: call to backup_section_task->define_settings()
    line 60 of /backup/util/plan/base_plan.class.php: call to base_task->set_plan()
    line 161 of /backup/moodle2/backup_plan_builder.class.php: call to base_plan->add_task()
    line 188 of /backup/moodle2/backup_plan_builder.class.php: call to backup_plan_builder::build_section_plan()
    line 101 of /backup/moodle2/backup_plan_builder.class.php: call to backup_plan_builder::build_course_plan()
    line 163 of /backup/util/factories/backup_factory.class.php: call to backup_plan_builder::build_plan()
    line 67 of /backup/util/plan/backup_plan.class.php: call to backup_factory::build_plan()
    line 463 of /backup/controller/backup_controller.class.php: call to backup_plan->build()
    line 149 of /backup/controller/backup_controller.class.php: call to backup_controller->load_plan()
    line 125 of /backup/backup.php: call to backup_controller->__construct()