by Ken Task.
The process of restoring from a .mbz file first un-compresses the .mbz (moodle backup zip) which might really be a gzip into a contenthash named (the 43f213b8c2569f39aaddf2c780f3e85f shown above) directory. It then uses the moodle_backup.xml file found in the un-archived files/folders as a road map to restore the course.
So ...
can you make a copy the .mbz file to a test directory AND 'unzip' it?
is there a moodledata/temp/ directory?
is there a moodledata/temp/backup/ directory?
Ownership permissions on moodledata/temp/backup directories need to be checked ... at least readable/writable by web server user.
'spirit of sharing', Ken