OS Slackware 12
Postfix version:
postconf mail_version
mail_version = 2.4.6

What may be causing the error: connection lost after DATE unknown

when it works:

April 20 07:23:50 mailserver postfix / smtpd [17515]: connect from unknown [192.168.6.213]
April 20 07:23:50 mailserver postfix / smtpd [17515]: E573527EF81: client = unknown [192.168.6.213]
April 20 07:23:50 mailserver postfix / cleanup [17518]: E573527EF81: message-id = <20200420102350.E573527EF81@aurora.br>
April 20 07:23:50 mailserver postfix / qmgr [9392]: E573527EF81: from = <monitoracao@aurora.br>, size = 1050, nrcpt = 1 (active queue)
April 20 07:23:50 mailserver postfix / smtpd [17515]: disconnect from the unknown [192.168.6.213]

when it doesn't work:

April 20 06:23:51 mailserver postfix / smtpd [15788]: connect from unknown [192.168.6.213]
April 20 06:23:51 mailserver postfix / smtpd [15788]: 6B88027EF81: client = unknown [192.168.6.213]
April 20 06:24:21 mailserver postfix / smtpd [15788]: connection lost after DATE unknown [192.168.6.213]


The two processes are running like this:

postfix 20446 0.0 0.8 30380 26072 ? S 16:11 0:00 smtpd -n smtps -t inet -u -s 2 -o smtpd_tls_wrappermode yes -o smtpd_tls_security_level encrypt -o smtpd_sasl_auth_enable yes -o smtpd_recipient_restrictions $smtps_recipient_restrictions
postfix 20448 0.0 0.8 30284 26016 ? S 16:11 0:00 smtpd -n submission -t inet -u -s 2 -o smtpd_tls_security_level encrypt -o smtpd_sasl_auth_enable yes -o smtpd_recipient_restrictions $submission_recipient_restrictions