External authentication times out when trying to match group membership.

Issue

• External authentication times out when trying to match group membership. If the user tries again a few hours later they can get in just fine. It looks like a timeout issue when checking user groups in LDAP.
• Error:

[----] W, [2015-12-02T11:50:50.312853 #29267:5bbe90]  WARN -- : <AuditFailure> MIQ(User.save_successful_logon) userid: [user-example.com] - Authentication failed for userid user-example.comx, unable to match user's group membership to an EVM role
[----] W, [2015-12-02T11:50:50.313079 #29267:5bbe90]  WARN -- : MIQ(User#save_successful_logon) User: [user-example.com]: Authentication failed for userid user-example.com, unable to match user's group membership to an EVM role
[----] I, [2015-12-02T11:50:50.319492 #29267:5bbe90]  INFO -- : <AuditSuccess> MIQ(User.authenticate_httpd) userid: [user-example.com] - Authentication successful for user user-example.com