This bug report is similar to this issue:
https://www.dovecot.org/list/dovecot/2017-May/108116.html

I know it is not enough info, but every kill follows with this info:
Feb 28 16:57:50 server dovecot[1511]: auth-worker: Fatal: master: service(auth-worker): child 17009 killed with signal 11 (core dumps disabled - https://dovecot.org/bugreport.html#coredumps)
Feb 28 16:57:50 server kernel: traps: auth[17009] general protection ip:7fd5d3ae9a64 sp:7fff0a781dc0 error:0 in libmariadb.so.3[7fd5d3add000+26000]

It looks like the error is related to the libmariadb.so, of course I am using integration with auth sql.

The configuration is like this:
# 2.3.4.1 (f79e8e7e4): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.4 ()
# OS: Linux 4.19.0-2-amd64 x86_64 Debian buster/sid ext4
# Hostname: p3x-dc.example.com
auth_mechanisms = plain login
mail_location = maildir:/var/mail/vhosts/%d/%n
mail_plugins = quota
mail_privileged_group = mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    auto = subscribe
    special_use = \Drafts
  }
  mailbox Junk {
    auto = subscribe
    autoexpunge = 30 days
    special_use = \Junk
  }
  mailbox Sent {
    auto = subscribe
    special_use = \Sent
  }
  mailbox Trash {
    auto = subscribe
    autoexpunge = 30 days
    special_use = \Trash
  }
  prefix = 
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
plugin {
  quota = maildir:User quota
  quota_grace = 10%%
  quota_max_mail_size = 100M
  quota_rule = *:storage=1G
  quota_rule2 = Trash:storage=+100M
  sieve = /etc/dovecot/sieve.conf
}
protocols = imap lmtp pop3
service auth-worker {
  user = vmail
}
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-userdb {
    mode = 0666
    user = vmail
  }
  user = dovecot
}
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}
service pop3-login {
  inet_listener pop3 {
    port = 0
  }
  inet_listener pop3s {
    port = 995
    ssl = yes
  }
}
service quota-status {
  client_limit = 1
  executable = quota-status -p postfix
  inet_listener {
    port = 12340
  }
}
ssl = required
ssl_ca = </etc/ssl/example.com/ca.cer
ssl_cert = </etc/ssl/example.com/fullchain.cer
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n
  driver = static
}
protocol lmtp {
  auth_socket_path = /var/run/dovecot/auth-master
  mail_plugins = quota sieve
}
protocol imap {
  mail_plugins = quota imap_quota
}


Patrik
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