The UninstallChart function checks whether a helm release exists before it deletes it. However, the function that checks for the existence of the release, uses the helm list command to do so.

This helm list command unfortunately ignores releases that are in an unusual state (e.g. PendingUpgrade, PendingInstall, Failed, etc.), leading to the operator thinking that the release doesn't exist and thus doesn't need to be deleted.

The operator thus never cleans up failed releases. When a new Istio/IstioRevision is created, the reconciliation of this new resource will fail due to the existence of the helm release.