You can delete them properly in the UI if you select the project. I think it's some sort of a failback and maybe the projects get deleted automatically after a few days.

Deleting a service removes only that service, not the project itself. Your "fabulous-surprise" project still exists in your dashboard because only the service inside it was removed. To fully remove a project from your dashboard, open the project, go to Settings, then the Danger tab, and click "Delete Project". This will permanently delete the project and all its associated services, environments, and deployments.