The IM thick client is expected to display the "Cannot list LDAP groups" error when there are many LDAP groups configured on AD. This can be mitigated via the filter_group key in the AD Template section in the hub.cfg
The workaround for this issue is to filter the list of LDAP groups by modifying the 'filter_group' parameter in the hub configuration:
1. Backup the hub.cfg on the target hub that will perform the LDAP Authentication
2. Open the hub.cfg and update the 'filter_group' key
Default Value: (objectClass=group)
Updated Value to list group 1 and 2: (&(objectCategory=group)(|(cn=grp1)(cn=grp2)))
OR
Updated Value to list all groups starting with 'grp': (&(objectCategory=group)(cn=grp*))
3. Save the change and restarted the Hub