metrics server is failing to scrape metrics post occm upgrade

$ kubectl get po
E0908 12:22:12.728083  759650 memcache.go:287] couldn't get resource list for metrics.k8s.io/v1beta1: the server is currently unable to handle the request
...

$ kubectl get po -n kube-system | grep metrics
cern-magnum-metrics-server-6bf94ffcc-85dvj                   0/1     Running   0          3d19h

$ kubectl describe po -n kube-system cern-magnum-metrics-server-6bf94ffcc-85dvj | grep -A 6 Events

Events:
  Type     Reason     Age                        From     Message
  ----     ------     ----                       ----     -------
  Warning  Unhealthy  3m55s (x35092 over 3d19h)  kubelet  Readiness probe failed: HTTP probe failed with statuscode: 500