If you find you can no longer connect to your GKE cluster, and see a message like
executable gke-gcloud-auth-plugin not found
it may be that you need to refresh the kubeconfig, especially if you’ve made changes to your gcloud installation.
As per https://cloud.google.com/kubernetes-engine/docs/how-to/cluster-access-for-kubectl you can get credentials, which updates your kubeconfig, by running:
gcloud container clusters get-credentials CLUSTER_NAME --region=COMPUTE_REGION
If that doesn’t help, first make sure you can still connect to the cluster from a terminal using kubectl. Then try launching Lens from the same terminal, e.g. on a mac:
/Applications/Lens.app/Contents/MacOS/Lens
If this doesn’t help post your detailed issue here on the forum.