Virtual Machine Scale Sets: Custom Script Extension Failure — Instances Are Unhealthy

Problem description

I am experiencing issues with the Custom Script Extension on a virtual machine scale set. Multiple instances are reporting as unhealthy, and the extension seems to be failing during script download or execution. The script is hosted in Azure Blob Storage, accessed via a SAS URL, and the extension's status indicates a failure. I need assistance in diagnosing the exact failure cause and resolving the issue.

Environment

Azure Virtual Machine Scale Sets with multiple instances, using Custom Script Extension to run a PowerShell script hosted in Azure Blob Storage with a SAS URL. Region not specified.

What I've already tried

I have reviewed the extension deployment configuration, including the script location and SAS token. I confirmed that the script download from Blob Storage still works, and the script runs successfully when executed manually on individual VMs. I also verified that no other extensions are configured or sequenced after the Custom Script Extension. Attempted reinstallation of the extension and reimaging the affected instances, but the problem persists.

Current status

Several instances remain unhealthy, with the extension failing to execute the script. I am seeking guidance to identify the exact error messages and failure details from the extension logs, and steps to fix the extension or script access issues.