Servicemesh Grafana endpoint:3001/metrics stuck with HTTP bad status 400 (target down)

Issue

• The grafana which has been enabled through the service mesh control plane configuration shows one of the endpoints is always down with HTTP 400.

http://10.131.0.38:3001/metrics   <-- This is basically a OAuth_proxy container
down    app="grafana" chart="grafana" heritage="Tiller" instance="10.131.0.38:3001" job="kubernetes-pods" maistra_control_plane="istio-system" namespace="istio-system" pod_name="grafana-5c44ddfffc-ms9wl" pod_template_hash="5c44ddfffc" release="istio"  2.006s ago  3.475ms     server returned HTTP status 400 Bad Request