We are investigating an issue related to failures in builds that some of our customers may be experiencing with their XAML build definitions deploying to Azure. Our DevOps team is actively working on a fix, below are a few options that could be attempted as a workaround.
1. Under the Services Tab in the project admin page, update the Azure End Points used in the build definition by adding "Project Collection Build Service Accounts" to the "Endpoint Administrators" and "Endpoint Readers" group.
2. Use a scripted build instead of XAML.
We apologize for any inconvenience this may be causing.