What's your doveconf -n? I suppose this is coming either when stopping/reloading, or maybe auth process stops when it's been idling for 1 minute. Do you use Postfix/Exim (or something else) that authenticates via Dovecot?

# 2.3.7 (494d20bdc):
# OS: FreeBSD 12.0-RELEASE-p7 amd64  zfs
# Hostname: poseidon.cloudzeeland.nl

auth_mechanisms = plain login
disable_plaintext_auth = no
mail_location = mbox:/home/%u:INBOX=/var/mail/%u
mail_privileged_group = mail
passdb {
  driver = pam
}
protocols = imap
service auth {
  unix_listener auth-client {
    group = mail
    mode = 0660
    user = postfix
  }
  unix_listener auth-master {
    mode = 0666
  }
  user = xxxxx
}
service imap-login {
  inet_listener imap {
    address = xxx.xxx.xxx.xxx
  }
  inet_listener imaps {
    address = xxx.xxx.xxx.xxx
  }
}
ssl_ca = </usr/local/share/certs/ca-root-nss.crt
ssl_cert = </usr/local/etc/dehydrated/certs/xxxxx/fullchain.pem
ssl_cipher_list = HIGH:+TLSv1.2:+TLSv1.3
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  driver = passwd
}
protocol imap {
  imap_client_workarounds = delay-newmail tb-extra-mailbox-sep
}
protocol lda {
  mail_plugins = sieve
  postmaster_address = postmaster@mysite.com
  sendmail_path = /usr/sbin/sendmail

Yes, I do reload Dovecot once a day in a nightly cron event.