When deploying Prometheus for 3scale monitoring we are hitting this upstream bug of prometheus-operator https://github.com/prometheus-operator/prometheus-operator/issues/3164 since latest prometheus-operator available in openshift is v0.37, we should mention the workaround (defining serviceMonitorSelector).

apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  name: prometheus
spec:
  ...
  serviceMonitorSelector: {}