As mentioned previously, those backups actually succeed but are marked with a false-positive error state. I believe that since a real solution would involve codebase changes to this certificate error from surfacing in the first place, here’s a not-so-ideal one, but one you can use right now:
You should install the edit-status kube plugin and edit the state of whatever backup you’d like to use.
kubectl edit-status psmdb-backup NAME
Update the status.state field from error to ready, which would allow you to use it for a restore.