$ oc logs deployment/prometheus-operator -n openshift-monitoring | grep "duplicate port definition with" -C2
level=info ts=2023-10-08T01:44:40.586511278Z caller=operator.go:655 component=alertmanageroperator key=openshift-monitoring/main msg="sync alertmanager"
level=info ts=2023-10-08T01:44:40.626492507Z caller=operator.go:655 component=alertmanageroperator key=openshift-monitoring/main msg="sync alertmanager"
level=warn ts=2023-10-08T01:44:40.628520232Z caller=klog.go:96 component=k8s_client_runtime func=Warning msg="spec.template.spec.containers[5].ports[0]: duplicate port definition with spec.template.spec.containers[2].ports[0]"
level=info ts=2023-10-08T01:44:40.63072762Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
level=info ts=2023-10-08T01:44:40.91709494Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
--
level=info ts=2023-10-08T01:45:19.85277831Z caller=operator.go:655 component=alertmanageroperator key=openshift-monitoring/main msg="sync alertmanager"
level=info ts=2023-10-08T01:45:24.014118091Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
level=warn ts=2023-10-08T01:45:24.256334754Z caller=klog.go:96 component=k8s_client_runtime func=Warning msg="spec.template.spec.containers[5].ports[0]: duplicate port definition with spec.template.spec.containers[2].ports[0]"
level=info ts=2023-10-08T01:45:24.259230552Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
level=info ts=2023-10-08T01:45:24.50510448Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
--
level=info ts=2023-10-08T07:33:33.724893975Z caller=operator.go:1310 component=prometheusoperator key=openshift-monitoring/k8s statefulset=prometheus-k8s shard=0 msg="recreating StatefulSet because the update operation wasn't possible" reason="Forbidden: updates to statefulset spec for fields other than 'replicas', 'ordinals', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden"
level=info ts=2023-10-08T07:33:35.232445429Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
level=warn ts=2023-10-08T07:33:35.442232343Z caller=klog.go:96 component=k8s_client_runtime func=Warning msg="spec.template.spec.containers[5].ports[0]: duplicate port definition with spec.template.spec.containers[2].ports[0]"
level=info ts=2023-10-08T07:33:35.445827197Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"
level=info ts=2023-10-08T07:33:35.708322936Z caller=operator.go:1189 component=prometheusoperator key=openshift-monitoring/k8s msg="sync prometheus"

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[5].ports[0]}' | jq
{
  "containerPort": 10902,
  "name": "thanos-proxy",
  "protocol": "TCP"
}

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[2].ports[0]}' | jq
{
  "containerPort": 10902,
  "name": "http",
  "protocol": "TCP"
}

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[5].name}' 
kube-rbac-proxy-thanos

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[2].name}' 
thanos-sidecar

$ oc get clusterversion
NAME      VERSION                              AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.14.0-0.nightly-2023-10-06-234925   True        False         3h33m   Cluster version is 4.14.0-0.nightly-2023-10-06-234925

$ oc logs deployment/prometheus-operator -n openshift-monitoring | grep "duplicate port definition with" -C2
no result

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[5].ports[0]}' | jq
{
  "containerPort": 10902,
  "name": "thanos-proxy",
  "protocol": "TCP"
}

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[2].ports[0]}' | jq
{
  "containerPort": 10902,
  "name": "http",
  "protocol": "TCP"
}

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[5].name}'
kube-rbac-proxy-thanos

$ oc -n openshift-monitoring get sts prometheus-k8s -ojsonpath='{.spec.template.spec.containers[2].name}'
thanos-sidecar

$ oc get clusterversion
NAME      VERSION                              AVAILABLE   PROGRESSING   SINCE   STATUS
version   4.15.0-0.nightly-2023-10-06-123200   True        False         7h1m    Cluster version is 4.15.0-0.nightly-2023-10-06-123200

always in 4.15

1. check prometheus-operator logs 

"duplicate port definition" warning message in 4.15 prometheus-operator

we could close this bug, since it seems it's expected