Im trying to upgrade my Azure AKS cluster from version 1.8.1 to 1.8.6.

Deployment failed. Correlation ID: 09312a25-04f3-4e35-8f79-6b2337bb7f19. Operation failed with status: 200. Details: Resource state Failed

The output of command az aks upgrade --name myaks --resource-group myresourcegr --kubernetes-version 1.8.6

More output az aks show --name myaks --resource-group myresourcegr --output table

    Name     Location    ResourceGroup    KubernetesVersion    ProvisioningState    Fqdn
    -------  ----------  ---------------  -------------------  -------------------  -----------------------------------------
    myaks  westeurope  myresourcegr             1.8.6                Failed               myaks-81cf39b1.hcp.westeurope.azmk8s.io

Retrying the upgrade action I get always the same error

Edit

Output of command az aks get-versions -g myresourcegr -n myaks

{
  "agentPoolProfiles": [
    {
      "kubernetesVersion": "1.8.6",
      "name": null,
      "osType": "Linux",
      "upgrades": [
        "1.8.6"
      ]
    }
  ],
  "controlPlaneProfile": {
    "kubernetesVersion": "1.8.6",
    "name": null,
    "osType": "Linux",
    "upgrades": [
      "1.8.6"
    ]
  },
  "id": "/subscriptions/xxx-98ec-4db6-bfed-946d93a62a7c/resourcegroups/myresourcegr/providers/Microsoft.ContainerService/managedClusters/myaks/upgradeprofiles/default",
  "name": "default",
  "resourceGroup": "myresourcegr",
  "type": "Microsoft.ContainerService/managedClusters/upgradeprofiles"
}