I had a similar problem with my Raspberry Pi distro. I can’t provide you with an answer as to why if $items is null, why the back up contents show, but the way to restore your backup is to copy the backup file to
/var/spool/asterisk/backup and then use the backup/restore in the GUI to restore it selecting local server.
In my issue, the http upload simply did not work to restore the backup file.
Hope I helped.
John