We've confirmed that all systems are back to normal with no customer impact as of 1/17, 16:13 UTC. Our logs show the incident started on 1/16, 20:08 UTC and that during the ~20 hours that it took to resolve the issue all customers who attempted to view alerts would have experienced issues while trying to view alerts in the Azure portal.
Root Cause: The failure was due to a new version deployed to the region with a code regression.
Incident Timeline: 20 Hours & 5 minutes - 1/16, 20:08 UTC through 1/17, 16:13 UTC
We understand that customers rely on Metric Alerts as a critical service and apologize for any impact this incident caused.
Initial Update: Friday, 17 January 2020 15:22 UTC
We are aware of issues within Azure Monitors and are actively investigating. Some customers may experience issues while viewing the Alerts in the Azure Portal.
Work Around: None
Next Update: Before 01/17 18:30 UTC
We are working hard to resolve this issue and apologize for any inconvenience. -Monish