At 16:48 UTC September 25th, a configuration change was deployed causing traffic being unable to reach the PHP process for a small set of Drupal 8+ sites. Our on-call engineers were alerted to the issues and began remediating and preventing the issue from spreading to further sites. The majority of affected customers had service restored by 18:49 UTC.
As part of our review, we will be implementing changes to both our testing and monitoring procedures to reduce risk of future issues.