Hey Yanic,
There are usually many reasons a Flexible Environment app (previously, "Managed VM") could be taking a while to deploy or start up. You can check the status of the deployment / build process in the console using the link which is output by the SDK at the start of deployment. Could you expand on what you meant by saying that gcloud commands don't seem to do anything? And finally, what does it look like in the "Compute Engine > Instances" view of the Developers Console?
Cheers,
Nick
Cloud Platform Community Support