Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / lib / Drupal / Core / Database / TransactionOutOfOrderException.php

<?php

namespace Drupal\Core\Database;

/**
 * Exception thrown when a rollBack() resulted in other active transactions being rolled-back.
 */
class TransactionOutOfOrderException extends TransactionException implements DatabaseException {}