We currently create cluster scoped resources from the controller. Simon already cleaned up invalid owner references (cluster scoped must not be owned by namespaces scoped).
These resources will currently stay behind when a stack or the operator are deleted.

For example the alertmanager cluster role is created for every monitoring stack. Really its only needed once though and every stack creates a binding.

Moving the creation of, say the cluster role, to the bundle will also take care of the cleanup issue since OLM should clean up bundle resources on bundle removal.