The issue has now been resolved.
This happened while we were upgrading one of the components that are responsible for pushing logs to our log cluster. Unfortunately, due to a misconfiguration, the logs between 21:20 and 21:40 UTC did not make it to the cluster. There was no impact on email delivery. We have the logs for this period available to us. If you need any assistance, please reach out to firstname.lastname@example.org
and they will help.