Red Hat Directory Server: memberOf attribute of user does not show the groups this user belongs to

Issue

1. RHDS user dn: uid=testuser,ou=it,ou=academy,ou=People,dc=example,dc=com is a member of RHDS groups dn: cn=internal,ou=group,dc=example,dc=com and dn: cn=external,ou=group,dc=example,dc=com as seen in the uniqueMember attribute of these 2 groups.

# internal, group, example.com
dn: cn=internal,ou=group,dc=example,dc=com
uniqueMember: uid=testuser,ou=it,ou=academy,ou=People,dc=example,dc=com  <<<<==== this is the RHDS user


# internal, group, example.com
dn: cn=external,ou=group,dc=example,dc=com
uniqueMember: uid=testuser,ou=it,ou=academy,ou=People,dc=example,dc=com <<<===== this is the RHDS user
uniqueMember: uid=testuser2,ou=it,ou=academy,ou=People,dc=example,dc=com
 ter
objectClass: posixGroup
objectClass: groupOfUniqueNames
objectClass: top
cn: internal
gidNumber: 333400

2. But these 2 above groups are not shown in memberOf attribute of the RHDS user, although we have already enabled memberOf plugin in the RHDS server:

# dsconf rhds-instance plugin memberof status
Plugin 'MemberOf Plugin' is enabled  <<<<<============ we already enabled MemberOf plugin

# testuser, it, academy, People, example.com
dn: uid=testuser,ou=it,ou=academy,ou=People,dc=example,dc=com
gidNumber: 333400
htc: FALSE
sn: Test
department: internal 
homeDirectory: /home/users/it/internal/testuser
o: Red Hat
hpc: TRUE
physicalDeliveryOfficeName: Singapore
telephoneNumber: 68088203
cn: testuser
uidNumber: 105010
mail: testuser@internal.redhat.inc
objectClass: inetOrgPerson
objectClass: acrcPerson
objectClass: inetUser
objectClass: posixAccount
objectClass: shadowAccount
objectClass: organizationalPerson
objectClass: top
objectClass: person
company: Red Hat
givenName: Test User
ou: internal
uid: testuser
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