Red Hat Directory Server online backup returns successful but the backup folder is empty

Issue

1. Online backup command to backup RHDS server to a customized folder return successful:

# /usr/sbin/dsconf -D "cn=Directory Manager" ldaps://ldapserver.example.com -y /root/passwd  backup create /backup
The backup create task has finished successfully

2. Query backup task output:

dn: cn=backup_2023-04-24T13:38:33.194903,cn=backup,cn=tasks,cn=config
objectClass: top
objectClass: extensibleObject
nsarchivedir: /backup
nsdatabasetype: ldbm database
cn: backup_2023-04-24T13:38:33.194903
nsTaskCurrentItem: 0
nsTaskTotalItems: 1
nsTaskCreated: 20230424113833Z
nsTaskWarning: 0
nsTaskLog:: QmVnaW5uaW5nIGJhY2t1cCBvZiAnbGRibSBkYXRhYmFzZScKL2hvbWUvZHNhZG1pbi9zZXJ2ZXIvUkhMREFQX0lfMDQvYmFja3VwL2RzY29uZmJhY2t1cCBleGlzdHMuIFJlbmFtaW5nIHRvIC9ob21lL2RzYWRtaW4vc2VydmVyL1JITERBUF9JXzA0L2JhY2t1cC9kc2NvbmZiYWNrdXAuYmFrCkJhY2tlbmQgJ3VzZXJyb290JyBpcyBhbHJlYWR5IGluIHRoZSBtaWRkbGUgb2YgYW5vdGhlciB0YXNrIGFuZCBjYW5ub3QgYmUgZGlzdHVyYmVkLgpCYWNrdXAgZmluaXNoZWQu
nsTaskStatus: Backup finished.
nsTaskExitCode: 0

3. But the backup folder is empty:

# ls -l /backup
total 0

4. Message in the Directory Server Log

24/Apr/2023:13:38:33.207869047 +0200] - INFO - task_backup_thread - Beginning backup of 'ldbm database'
[24/Apr/2023:13:38:33.210553368 +0200] - INFO - ldbm_back_ldbm2archive - /backup exists. Renaming to /backup.bak
[24/Apr/2023:13:38:33.214152809 +0200] - WARN - ldbm_back_ldbm2archive - Backend 'userroot' is already in the middle of another task and cannot be disturbed.
[24/Apr/2023:13:38:33.218262551 +0200] - INFO - task_backup_thread - Backup finished.