How to restore missing Google App Engine Application
A google project was deleted and restored after about a week. In the image below there is a stopped app engine. Neither testing nor default exists anymore. Clicking on either throws a "Requested entity was not found" error in the browser console. Why do I see these as existing in the asset inventory and are searchable, but they do not seem to exists as actual App Engine applications and services? Are app engine applications deleted in as little as a week even when the project is restored?
Make sure that the app engine service status is "user disabled " , it's one of the reasons you can not use the previous available app engine or create a new app engine. Also try to disable that service and create a new app engine again.
Also check if Datastore is enabled and in-use for the project. App Engine cannot be deployed in a project that already has Datastore in-use. You can try creating a new App Engine application first and then create the Datastore in the same region.
If you enabled the app engine service and re-created a new app engine , and are still facing the same issue , then the only workaround would be to create a new project. Then you can create an App Engine in the same region you used before.
Also you need to consider that restoration takes more time to function as everything.
Also as @John Hanley suggested try to restart the instance and please check on the app engine logs.
Also take a look at this Documentation -1 and Documentation -2.
If the above steps doesn’t help, you may consider contacting google support as it may requires project inspection.