The issue has been checked in RHSSO 7.4.6 and 7.4.7
They are using PostgreSQL and LDAP for user federation.
LDAP configuration has a group-ldap-mapper with "Preserve Group Inheritance" turned on.
The exact error is:
Caused by: org.postgresql.util.PSQLException: ERROR: duplicate key value violates unique constraint "sibling_names"
Detail: Key (realm_id, parent_group, name)=(<realm_id>, , 100000000) already exists.