Varun,
As only a few users are seeing this problem it could be related to a few areas including referrals and/or large group memberships.
By default the gateway will follow referrals which can cause issues if the directory environment is being searched for the top level but all the users are expected in the local environment. You can disable this by setting the cluster wide property ldap.referral to ignore.
The large group membership is controlled through the cluster wide property ldap.group.searchMaxResults which in later versions is set to 1000 but you may need to increase. Lastly I would also look at the nesting setting in the LDAP Provider on the Advanced Configuration page as the nesting may be too deep so look to set this to 1.
Sincerely,
Stephen Hughes
Broadcom Support