Can you please attach the YAML for this resource, generated with "oc get -o yaml"?

It is in the description, but probably not cleat, sorry :)
here is the full state:

$ oc get networkmap/node-05-missing-name -oyaml
apiVersion: forklift.konveyor.io/v1alpha1
kind: NetworkMap
metadata:
  creationTimestamp: "2021-04-25T14:22:11Z"
  generation: 1
  managedFields:
  - apiVersion: forklift.konveyor.io/v1alpha1
    fieldsType: FieldsV1
    fieldsV1:
      f:spec:
        f:map: {}
      f:status:
        .: {}
        f:conditions: {}
        f:observedGeneration: {}
    manager: manager
    operation: Update
    time: "2021-04-25T14:22:11Z"
  - apiVersion: forklift.konveyor.io/v1alpha1
    fieldsType: FieldsV1
    fieldsV1:
      f:spec:
        .: {}
        f:provider:
          .: {}
          f:destination:
            .: {}
            f:name: {}
            f:namespace: {}
          f:source:
            .: {}
            f:name: {}
            f:namespace: {}
    manager: oc
    operation: Update
    time: "2021-04-25T14:22:11Z"
  name: node-05-missing-name
  namespace: openshift-rhmtv
  resourceVersion: "7401655"
  selfLink: /apis/forklift.konveyor.io/v1alpha1/namespaces/openshift-rhmtv/networkmaps/node-05-missing-name
  uid: aa1e81d0-005b-45d9-8512-90bb3fed6bcb
spec:
  map:
  - destination:
      type: pod
    source:
      id: network-14
  - destination:
      type: multus
    source:
      id: network-13
  provider:
    destination:
      name: host
      namespace: openshift-rhmtv
    source:
      name: node-05
      namespace: openshift-rhmtv
status:
  conditions:
  - category: Required
    lastTransitionTime: "2021-04-27T08:07:01Z"
    message: The network map is ready.
    status: "True"
    type: Ready
  observedGeneration: 1

Thanks. Indeed, the description is not clear whether mapping are arrays. With the YAML, it's less ambiguous.

This is not a blocker and will not happen when using the UI. Targeting 2.1.0.

This appears to have been fixed already, possibly months ago. Could it be retested with a recent build?

spec:
  map:
  - destination:
      name: pod
      namespace: konveyor-forklift
      type: pod
    source:
      id: network-31
  - destination:
      namespace: konveyor-forklift
      type: multus
    source:
      id: network-34
  provider:
    destination:
      name: host
      namespace: konveyor-forklift
    source:
      name: boston
      namespace: konveyor-forklift
status:
  conditions:
  - category: Critical
    items:
    - network-34
    lastTransitionTime: "2021-06-16T20:33:11Z"
    message: Destination network not found.
    reason: NotFound
    status: "True"
    type: DestinationNetworkNotValid
  observedGeneration: 3
  references:
  - id: network-31
    name: VM Network
  - id: network-34
    name: VM_10G_Network

Please test with the mtv-operator-bundle-2.1.0-5 build / iib:85044.

verified:

2.10-17 / iib:87576


Spec:
  Map:
    Destination:
      Type:  pod
    Source:
      Id:  network-14
    Destination:
      Namespace:  default
      Type:       multus
    Source:
      Id:  network-13
  Provider:
    Destination:
      Name:       host
      Namespace:  openshift-mtv
    Source:
      Name:       node05
      Namespace:  openshift-mtv
Status:
  Conditions:
    Category:  Critical
    Items:
      default
    Last Transition Time:  2021-07-07T06:14:25Z
    Message:               Destination network not found.
    Reason:                NotFound
    Status:                True
    Type:                  DestinationNetworkNotValid
  Observed Generation:     1
  References:
    Id:    network-14
    Name:  VM Network
    Id:    network-13
    Name:  Mgmt Network
Events:
  Type     Reason                      Age   From        Message
  ----     ------                      ----  ----        -------
  Warning  DestinationNetworkNotValid  9s    networkMap  Destination network not found.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Migration Toolkit for Virtualization 2.1.0), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2021:3278