Hi!

The classification store keys are not deleted properly if someone deletes them via the backend interface. And the reason is probably because they actually never get deleted:

$config = Classificationstore\KeyConfig::getById($id);
//        $config->delete();
$config->setEnabled(false);
$config->save();

See:

This might have something to do with the behavior when keys are actually deleted, e.g. when someone calls $config->delete(), as this deletes the key itself, its group relations but not any data object relations, resulting in an exception when someone accesses a related data object.