azure python extension fail on 'conflict' in deployment ARM

Question

I am using template for azure web app . net deployment. I need python extension to deploy as well after MSbuild is deployed. This script works when resource group and app service plan is new, but it fails when there are already web apps running on resource group/app service plan.

{
    "status": "Failed",
    "error": {
        "code": "ResourceDeploymentFailure",
        "message": "The resource operation completed with terminal provisioning state 'Canceled'."
    }
}

any tip on what's the conflict at the background thread.