"duplicate" PrometheusRule objects observed. 

~~~    
oc get -n openshift-monitoring prometheusrules.monitoring.coreos.com
NAME                                           AGE
alertmanager-main-rules                        2y149d
bis-custom-alertingrules-bd731a                153d
bis-custom-alertingrules-d4367e                509d
~~~

one with 

~~~
labels:
    app.kubernetes.io/component: alerting-rules-controller
    app.kubernetes.io/name: cluster-monitoring-operator
    app.kubernetes.io/part-of: openshift-monitoring
    app.kubernetes.io/version: 4.16.38
    prometheus: k8s
    role: alerting-rules
~~~

the other one with 

~~~
labels:
    app.kubernetes.io/component: alerting-rules-controller
    app.kubernetes.io/name: cluster-monitoring-operator
    app.kubernetes.io/part-of: openshift-monitoring
    app.kubernetes.io/version: 4.14.29
    prometheus: k8s
    role: alerting-rules
~~~

they both have an ownerReferences pointing to the same uid 8a7ef0f2-db18-4c10-9a56-3df02e4885a7
The rules have changed over time, and the customer observe that in the prometheus-k8s-rulefiles-0 configmap, managed by the operator, there are 2 versions of some of those rules

 4.16    

   Unable to reproduce  

Example: the bis-PersistentVolumeUsageCritical alert definition
It's defined only once in the Alertingrules config, but found twice in the prometheus-k8s-rulefiles-0 configmap
The order of those duplicate entries in the prometheus-k8s-rulefiles-0 configmap changes between clusters, so effectively in some clusters we are using the new version of the rule, while in others we are still using the old version of the rule.   

Updated rules should replace existing rules