We've confirmed that all systems are back to normal with no customer impact as of 12/30, 04:04 UTC. Our logs show the incident started on 12/30, 00:28 UTC and that during the 3 hours and 36 minutes that it took to resolve the issue customers in East US region might have experienced Alerting failure or Delayed alerts .
Root Cause: The failure was due to an issue in one of the dependent services.
Incident Timeline: 3 Hours & 36 minutes - 12/30, 00:28 UTC through 12/30, 04:04 UTC
We understand that customers rely on Log Analytics as a critical service and apologize for any impact this incident caused.