What version of Moodle?
For that matter what versions of PHP and MySQL/MariaDB as well!
If an old version of Moodle - no longer support - and this is a bug, it won't be fixed.
Unfortunately, Bitnami isn't flexible in that one cannot upgrade supports for moodle ... like PHP and DB server - upgrading a moodle could mean upgrading the entire Bitnami stack!
What if you turned on debugging all the way to max? Does moodle report any more info?
Still, the command you show you issued.
The backup file is stored in /bitnami/moodle/backup/name_of_ backup .mbz.
That appears to be an .mbz file in moodle code - not coming from an .mbz file stored in moodledata/ or else where. Thus one might get strange errors - ownerships/permissions.
Restores begin with backups ... so suggest using a file system repository in moodle.
The directory would be in moodledata/repository/nameyougiveit to make the backup.
Issue the command to backup the course with destination to be the file system repository you set up.
The restore command then would point to that .mbz file in the file system repository you set up.
Using the file system repo there is no download/upload and it's only PHP talking to the DB server. The file system repo given liberal ownerships/permission as all files in moodledata are.
'SoS', Ken