I observed that many times clusters can be stuck in Deleting state. This can happen both after a successful creation and subsequent deletion, or a removal of an Active cluster. It is not easy to give a consistent reproducer.
In those cases, heat shows an empty stack (tested with `openstack stack list --hidden --nested`).
I suspect that the engine loses the notification of the cleanup from heat and it does not switch the status.
I'm not sure if, apart from heat cleaning up the stack, some other steps are required by the engine in order to cleanup a cluster. If it is the case, those additional steps should be (re)triggered as well when the engine detects that the heat stack is empty.
The configuration key cleanup_time_for_incomplete_clusters does not apply in this case as Delete is considered a "final" state for it.
Found in many versions, I can remember for sure from Liberty; hitting frequently on Newton (Red Hat OpenStack Platform on Red Hat Enterprise Linux).