dovecot+ldap with keepalive

[Maciej Milaszewski]

Hi
I have dovecot-2.36.4 (director +5 nodes) - backend to auth is
openldap+keepalived to second ldap

For test i shutdown my ldap server - keepalive  works perfectly VIP
switched - ldapserach works ok (all connect to second ldap)
but I noticed strange dovecot behavior - some user get "no response" or
"waiting waiting"

in dovecot i use:
auth_cache_negative_ttl = 5 mins
auth_cache_size = 20 M
auth_cache_ttl = 5 mins

service lmtp {
  inet_listener lmtp {
    address = 127.0.0.1 10.0.100.4
    port = 24
  }
  process_min_avail = 5

protocol lmtp {
  auth_socket_path = director-userdb
  mail_plugins = quota expire notify mail_log
  passdb {
    args = proxy=y nopassword=y port=24
    driver = static
    name =
  }
  syslog_facility = local3
}


in ldap server i have:
idletimeout     256

Any idea ?