I'm currently using a step with pipe atlassian/google-app-engine-deploy:1.1.1. I'd been using v0.4.1 fine, but noticed it was stripping out the appengine-api-1.0-sdk JAR, and assumed that was the issue.
Dropping back down from 1.1.1 to 1.0.0 works, so I can only assume it's an issue/bug with the latest version when using Java:
The component [app-engine-java] is required for staging this application.
ERROR: (gcloud.app.deploy) You cannot perform this action because the Google Cloud CLI component manager is disabled for this installation. You can run the following command to achieve the same result for this installation:
sudo apt-get install google-cloud-sdk-app-engine-java
✖ Deployment failed.
I'd raise this as a bug, but you (Atlassian) make it a UX nightmare to do so.