We've confirmed that all systems are back to normal with no customer impact as of 5/18, 09:30 UTC. Our logs show the incident started on 5/18, 07:45 UTC and that during the 1 hour and 45 minutes that it took to resolve the issue some of customers may have experienced Missed Alerts issue in South UK region.
Root Cause: The failure was due to an issue in one of our dependent services.
Incident Timeline: 1 Hours & 45 minutes - 5/18, 07:45 UTC through 5/18, 09:30 UTC
We understand that customers rely on Azure Log Analytics as a critical service and apologize for any impact this incident caused.