We've confirmed that all systems are back to normal with no customer impact as of 10/28, 02:08 AM UTC. Our logs show the incident started on 10/27, 18:25 PM UTC and that during the impact hours that it took to resolve the issue, Customers in Multiple regions would have experienced errors viewing data in the Azure Portal.
Root Cause: We have determined the underlying cause to be due to configuration change in a backend service upon which Azure Monitor, Log Analytics and Application insights relies upon.
Incident Timeline: 10/27, 18:25 UTC through 10/28, 02:08 UTC
We understand that customers rely on Azure Monitor as a critical service and apologize for any impact this incident caused.
Update: Thursday, 28 October 2021 01:13 UTC
Root cause has been isolated to one of backend service root cert rotation that was rolled out which was impacting Azure Monitor, Azure Log Analytics or Azure Application Insights. To address this issue we have deployed a cert fix to the affected regions. Some customers may experience errors viewing data in the Azure Portal and we estimate 2 hours before all issues are addressed.