When you try to deploy a version of your APP to Google App Engine using a pipeline on Azure DevOps, if the deployment step itself is failed, normally the new version may not be deployed to App Engine. You just need to retry the pipeline.
However, if the deployment step has completed successfully, but one of the subsequent steps or jobs is failed and caused the pipeline failed, the new version has been deployed to App Engine. In this situation, you may not able to redeploy the same version to App Engine.
solved How to create version number in Google App Engine