by Ken Task.
Well, sorry to hear that! More sluething ...
Moodle uses the moodledata/temp/backup/ directory for backups and restores. Success backups/restores leave a 0 byte .log file. Unsuccessful backups/restores leave a larger than 0 byte .log file - and a contenthash named directory. Inspect the .log file for a clue. Might look into that contenthash named directory for a moodle_backup.xml file - that's the roadmap to the course contents and is used in both backups and restores. If something exist in the .xml file but one cannot find the corresponding item in the rest of the folders/files, there's your culprit. Now what to do about it ... ????
'spirit of thinkering', Ken