StalePersistentVolumeClaim triggers for any ephemeral volume most likely due to the fact that ephemeral volumes do not have a matching claimName in the pod but rather the volume template itself.
This also manifests in the fact that "Used by" is empty for any emphemeral volume in eg .kubectl describe pvc
All this leads to kube_pod_spec_volumes_persistentvolumeclaims_info missing which then triggers the alert.
No idea where is the right place to fix this yet tbh.