Ansible's idempotency is an illusion. Removing an item from a playbook will practically cause it to be "forgotten" by Ansible, but left on machines where it was deployed previously. While there are mechanisms to remove stale items (state=absent), in practice it takes Spock-level discipline to do this properly. Playbooks are also not tied to a particular Ansible version, meaning just upgrading Ansible can cause changes even though your definitions are still the same. In my experience Ansible promises consistent environments, but consistently fails to deliver.