Could be the data was not written to tape or the backup was done via an agent and the restore is not using the agent.
Under Restore by Session do you see all the directories and file that should be there?
Run a Scan with it configured to Log All Details under Options to write to the job log all the directories and files in the session or on the tape.
Since it was an upgrade the old activity log will be there. It will be called brightstor.log or activity.log in the Log subdirectory. Check the log for the backup to verify the data was written to tape.
For the second option just make sure the correct agent is selected when setting up the restore job.