In my environment, I have used Kasten version v6.0.12 to back up Redhat Openshift Virtualization Virtual machine. No problem on using snapshot however encounter an error when trying to restore from S3.
After troubleshooting, realized that S3 backup data is a reference to snapshot backup data which has expired/removed. Well, it is not supposed to and reported as a bug for the next release fix.
For a workaround, you need to create a TransformSet. Refer to the below diagram to configure it and apply it when doing a restoration. [Click the image to view in large mode]