dovecot - Sep 2018 - Auth process sometimes stop responding after upgrade

Hi all;
I've upgraded a ring of dovecot directors from 2.2.15 to 2.2.36. After the
upgrade I've got
some instability: a few time per day per server, seemly at random, the auth
process stop
responding and the clients cannot authenticate any more:

Sep  6 14:45:51 imap-front13 dovecot: pop3-login: Warning: Auth process not
responding,
delayed sending initial response (greeting): user=<>, rip=xx.xx.xx.xx,
lip=xx.xx.xx.xx, TLS,
session=<1HVqRTN10MNTie+S>

I can't figure it out.... Any hints?

This is my configuration:


# 2.2.36 (1f10bfa63): /usr/local/etc/dovecot/dovecot.conf
# OS: Linux 3.2.0-4-686-pae i686 Debian 7.11 
# Hostname: imap-front13.mailfarm.interac.it
auth_mechanisms = plain login digest-md5 cram-md5 apop scram-sha-1
auth_verbose = yes
auth_verbose_passwords = plain
auth_worker_max_count = 50
base_dir = /var/run/dovecot/
default_login_user = nobody
director_doveadm_port = 9091
director_mail_servers = 192.168.1.142 192.168.1.143 192.168.1.144 192.168.1.145 
192.168.1.216 192.168.1.217 192.168.1.218 192.168.1.219
director_servers = 212.183.164.157 212.183.164.158 212.183.164.159
212.183.164.160
listen = *
passdb {
  args = /usr/local/etc/dovecot/sql.conf
  driver = sql
}
protocols = imap pop3
service director {
  fifo_listener login/proxy-notify {
    mode = 0666
  }
  inet_listener {
    port = 9090
  }
  unix_listener director-userdb {
    mode = 0600
  }
  unix_listener login/director {
    mode = 0666
  }
}
service imap-login {
  executable = imap-login director
  service_count = 0
  vsz_limit = 128 M
}
service pop3-login {
  executable = pop3-login director
  service_count = 0
  vsz_limit = 128 M
}
ssl_cert = </usr/local/etc/dovecot/qcom.wildcard.pem
ssl_cipher_list = ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-
SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-
AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-
SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-
SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-
SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-
AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-
SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-
SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!
PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA
ssl_dh_parameters_length = 2048
ssl_key =  # hidden, use -P to show it
ssl_parameters_regenerate = 1 weeks
ssl_prefer_server_ciphers = yes
ssl_protocols = !SSlv2 !SSLv3
syslog_facility = local5
userdb {
  driver = prefetch
}


*Simone Lazzaris*
*Qcom S.p.A.*
simone.lazzaris at qcom.it[1] | www.qcom.it[2]
* LinkedIn[3]* | *Facebook[4]*
[5] 






--------
[1] mailto:simone.lazzaris at qcom.it
[2] https://www.qcom.it
[3] https://www.linkedin.com/company/qcom-spa
[4] http://www.facebook.com/qcomspa
[5] https://www.qcom.it/includes/email-banner.gif
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