OpenShift update Service pods unable to start due to ImagePullBackOff error and unable to fetch the graph data

Issue

• OpenShift Update Service (OSUS) pods get stuck in pending state.

$ oc -n openshift-update-service get pods

NAME                                      READY         STATUS   RESTARTS              AGE     
update-service-oc-mirror-xxxxxx           0/2           Pending   0                    8d            <----
update-service-oc-mirror-xxxxxx           2/2           Running   0                    118d         
updateservice-operator-xxxxxx             1/1           Running   0                    118d

• The YAML definition of the failing pod shows the following error :-

$ oc -n openshift-update-service get pod update-service-oc-mirror-xxxxxx -oyaml

state:
      waiting:
        message: Back-off pulling image "{LCOAL_REGISTRY}/{LOCAL_REPOSITORY}@sha256:xxxxxx"
        reason: ImagePullBackOff

• Trying to pull the image manually results in Manifests unknown alert :-

Trying to pull {LCOAL_REGISTRY}/{LOCAL_REPOSITORY}@sha256:xxxxxx
Error reading manifest : manifest unknown