I have upgraded my 3 master and 6 nodes kubernetes cluster from kubernetes version 1.17.5 to 1.18.0 and post upgrade kubernetes-dashboard stopped working with below error :

{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {

  },
  "status": "Failure",
  "message": "no endpoints available for service \"kubernetes-dashboard\"",
  "reason": "ServiceUnavailable",
  "code": 503
}

dashboard status Before upgrade:

kubectl get deployment kubernetes-dashboard --namespace=kubernetes-dashboard
NAME                   READY   UP-TO-DATE   AVAILABLE   AGE
kubernetes-dashboard   1/1     1            1           35m

kubectl describe service kubernetes-dashboard --namespace=kubernetes-dashboard
Name:              kubernetes-dashboard
Namespace:         kubernetes-dashboard
Labels:            k8s-app=kubernetes-dashboard
Annotations:       Selector:  k8s-app=kubernetes-dashboard
Type:              ClusterIP
IP:                10.y.y.y
Port:              <unset>  443/TCP
TargetPort:        8443/TCP
Endpoints:         192.168.x.x:8443
Session Affinity:  None
Events:            <none>

kubectl --namespace=kubernetes-dashboard get ep kubernetes-dashboard
NAME                   ENDPOINTS            AGE
kubernetes-dashboard   192.168.x.x:8443   36m

dashboard status After Upgrade:

kubectl get deployment kubernetes-dashboard --namespace=kubernetes-dashboard
NAME                   READY   UP-TO-DATE   AVAILABLE   AGE
kubernetes-dashboard   0/1     0            0           88m

kubectl describe service kubernetes-dashboard --namespace=kubernetes-dashboard
Name:              kubernetes-dashboard
Namespace:         kubernetes-dashboard
Labels:            k8s-app=kubernetes-dashboard
Annotations:       <none>
Selector:          k8s-app=kubernetes-dashboard
Type:              ClusterIP
IP:                10.y.y.y
Port:              <unset>  443/TCP
TargetPort:        8443/TCP
Endpoints:         <none>
Session Affinity:  None
Events:            <none>

kubectl --namespace=kubernetes-dashboard get ep kubernetes-dashboard
NAME                   ENDPOINTS   AGE
kubernetes-dashboard   <none>      88m

No pods are present under namespace kubernetes-dashboard while it was there before upgrade. Here is some part of kubernetes-dashboard deployment yaml output :

    manager: kubectl
    operation: Update
    time: "2020-05-14T20:56:04Z"
  name: kubernetes-dashboard
  namespace: kubernetes-dashboard
  resourceVersion: "66272"
  selfLink: /apis/apps/v1/namespaces/kubernetes-dashboard/deployments/kubernetes-dashboard
  uid: 11d1b3e7-b333-4cf0-a542-a72a09f3d56a
spec:
  progressDeadlineSeconds: 600
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      k8s-app: kubernetes-dashboard
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      creationTimestamp: null
      labels:
        k8s-app: kubernetes-dashboard
    spec:
      containers:
      - args:
        - --auto-generate-certificates
        - --namespace=kubernetes-dashboard
        image: kubernetesui/dashboard:v2.0.0
        imagePullPolicy: Always
        livenessProbe:
          failureThreshold: 3
          httpGet:
            path: /
            port: 8443
            scheme: HTTPS
          initialDelaySeconds: 30
          periodSeconds: 10
          successThreshold: 1
          timeoutSeconds: 30
        name: kubernetes-dashboard
        ports:
        - containerPort: 8443
          protocol: TCP
        resources: {}
        securityContext:
          allowPrivilegeEscalation: false
          readOnlyRootFilesystem: true
          runAsGroup: 2001
          runAsUser: 1001
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        volumeMounts:
        - mountPath: /certs
          name: kubernetes-dashboard-certs
        - mountPath: /tmp
          name: tmp-volume
      dnsPolicy: ClusterFirst
      nodeSelector:
        kubernetes.io/os: linux
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      serviceAccount: kubernetes-dashboard
      serviceAccountName: kubernetes-dashboard
      terminationGracePeriodSeconds: 30
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/master
      volumes:
      - name: kubernetes-dashboard-certs
        secret:
          defaultMode: 420
          secretName: kubernetes-dashboard-certs
      - emptyDir: {}
        name: tmp-volume
status:
  conditions:
  - lastTransitionTime: "2020-05-14T20:56:04Z"
    lastUpdateTime: "2020-05-14T20:56:04Z"
    message: Created new replica set "kubernetes-dashboard-7b544877d5"
    reason: NewReplicaSetCreated
    status: "True"
    type: Progressing
  - lastTransitionTime: "2020-05-14T20:56:04Z"
    lastUpdateTime: "2020-05-14T20:56:04Z"
    message: Deployment does not have minimum availability.
    reason: MinimumReplicasUnavailable
    status: "False"
    type: Available
  - lastTransitionTime: "2020-05-14T20:56:04Z"
    lastUpdateTime: "2020-05-14T20:56:04Z"
    message: 'pods "kubernetes-dashboard-7b544877d5-" is forbidden: unable to validate
      against any pod security policy: []'
    reason: FailedCreate
    status: "True"
    type: ReplicaFailure
  observedGeneration: 1
  unavailableReplicas: 1