Not able to login into server even as root. /var/log/secure gives an error 'error retrieving information about user root'

Issue

• Not able to login into server even as root.  While tying to login remotely via ssh we try ssh, it gives an error connection closed by remote host. After rebooting the system, issue was fixed.

• /var/log/secure shows below error at the time of issue.

  Mar 23 18:58:55 host701 login: pam_unix(login:auth): check pass; user unknown
  Mar 23 18:58:55 host701 login: pam_unix(login:auth): authentication failure; logname= uid=0 euid=0 tty=tty1 ruser= rhost=
  Mar 23 18:58:55 host701 login: pam_succeed_if(login:auth): error retrieving information about user root
  Mar 23 18:58:58 host701 login: FAILED LOGIN 1 FROM (null) FOR root, User not known to the underlying authentication module
  

• /var/log/message shows below error related to nss_ldap

  Mar 23 17:26:01 host701 nscd: nss_ldap: reconnected to LDAP server ldaps://ldaps.dir.ucb-example.com/ after 1 attempt
  Mar 23 17:45:37 host701 nscd: nss_ldap: reconnected to LDAP server ldaps://ldaps.dir.ucb-example.com/ after 1 attempt
  Mar 23 18:04:41 host701 nscd: nss_ldap: reconnected to LDAP server ldaps://ldaps.dir.ucb-example.com/ after 1 attempt
  Mar 23 18:25:46 host701 nscd: nss_ldap: reconnected to LDAP server ldaps://ldaps.dir.ucb-example.com/ after 1 attempt