longhorn: [Question] MountVolume.SetUp failed - There is no block device frontend

I am running longhorn 1.0.2 in a self managed kubernetes cluster Everything works fine. But I observer the following warning when I launch a new POD (in this case a postgresdb)

MountVolume.SetUp failed for volume "xxx : rpc error: code = InvalidArgument desc = There is no block device frontend for volume xxx

These are the events form the pod description after successful deployment:

 Events:                                                                                                                                                                   │
│   Type     Reason                  Age                  From                      Message                                                                                 │
│   ----     ------                  ----                 ----                      -------                                                                                 │
│   Warning  FailedScheduling        <unknown>            default-scheduler         persistentvolumeclaim "dbdata" not found                                                │
│   Warning  FailedScheduling        <unknown>            default-scheduler         persistentvolumeclaim "dbdata" not found                                                │
│   Warning  FailedScheduling        <unknown>            default-scheduler         running "VolumeBinding" filter plugin for pod "postgres-6f8fc59cd8-p5p4g": pod has unbound immediate PersistentVolumeClaims                                                                                                                                      │
│   Normal   Scheduled               <unknown>            default-scheduler         Successfully assigned documents-imixs-com/postgres-6f8fc59cd8-p5p4g to ixchel-worker-2  │
│   Normal   SuccessfulAttachVolume  4m11s                attachdetach-controller   AttachVolume.Attach succeeded for volume "documents-imixs-com-dbdata"                   │
│   Warning  FailedMount             4m6s (x2 over 4m7s)  kubelet, ixchel-worker-2  MountVolume.SetUp failed for volume "documents-imixs-com-dbdata" : rpc error: code = InvalidArgument desc = There is no block device frontend for volume documents-imixs-com-dbdata                                                                              │
│   Normal   Pulled                  4m4s                 kubelet, ixchel-worker-2  Container image "postgres:9.6.1" already present on machine                             │
│   Normal   Created                 4m4s                 kubelet, ixchel-worker-2  Created container postgres                                                              │
│   Normal   Started                 4m4s                 kubelet, ixchel-worker-2  Started container postgres   

My PVC/PV configuation looks like this:

kind: PersistentVolume
apiVersion: v1
metadata:
  name: documents-imixs-com-dbdata
spec:
  capacity:
    storage: 2Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  claimRef:
    namespace: documents-imixs-com
    name: dbdata
  csi:
    driver: driver.longhorn.io
    fsType: ext4
    volumeHandle: xxx
  storageClassName: longhorn-durable

----
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dbdata
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn-durable
  resources:
    requests:
      storage: 2Gi
  volumeName: "xxx"

Is this warning something I should be concerned of or can I still ignore this warning?

Thanks for Help

=== Ralph