Unfortunately, alert notifications for some alerts were not sent out from 2019-03-26 16:03:51 UTC to 2019-03-28 08:51:00 UTC. This was because a thread dealing with the notification process was killed but a new thread was not spawned. The issue has now been fixed and all alert notifications are now working as expected. Engineering will investigate further to identify the root cause of this issue. We will also add extra monitoring on our own systems so that we are notified if such issues happen again.