After upgrading Zabbix Agent and Server to 4.4.2 this morning, the agent starts crashing as long as the Server is reachable for them. This affects remote agents as well as the agent installed on the server itself. Even the last one uses psk, as I streamlined the configuration as much as possible.

zabbix:~# zabbix_agentd --version
zabbix_agentd (daemon) (Zabbix) 4.4.2
Revision 6d7579cc01 25 November 2019, compilation time: Nov 25 2019 16:07:39Copyright (C) 2019 Zabbix SIA
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it according to
the license. There is NO WARRANTY, to the extent permitted by law.This product includes software developed by the OpenSSL Project
for use in the OpenSSL Toolkit (http://www.openssl.org/).Compiled with OpenSSL 1.1.1c 28 May 2019
Running with OpenSSL 1.1.1d 10 Sep 2019

zabbix:~# zabbix_server --version
zabbix_server (Zabbix) 4.4.2
Revision 6d7579cc01 25 November 2019, compilation time: Nov 25 2019 16:07:39Copyright (C) 2019 Zabbix SIA
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it according to
the license. There is NO WARRANTY, to the extent permitted by law.This product includes software developed by the OpenSSL Project
for use in the OpenSSL Toolkit (http://www.openssl.org/).Compiled with OpenSSL 1.1.1c 28 May 2019
Running with OpenSSL 1.1.1d 10 Sep 2019

zabbix:~# cat /etc/zabbix/zabbix_agentd.conf | grep -v "^#" | grep .
PidFile=/var/run/zabbix/zabbix_agentd.pid
LogType=system
LogFile=/var/log/zabbix/zabbix_agentd.log
LogFileSize=0
DebugLevel=3
Server=127.0.0.1
ServerActive=127.0.0.1
Hostname=Zabbix server
Include=/etc/zabbix/zabbix_agentd.d/*.conf
TLSConnect=psk
TLSAccept=psk
TLSPSKIdentity=PSK
TLSPSKFile=/etc/zabbix/psk

zabbix:~# cat /etc/zabbix/zabbix_server.conf | grep -v "^#" | grep .
LogType=system
LogFile=/var/log/zabbix/zabbix_server.log
LogFileSize=0
PidFile=/var/run/zabbix/zabbix_server.pid
SocketDir=/var/run/zabbix
DBName=...
DBUser=...
DBPassword=...
SNMPTrapperFile=/var/log/snmptrap/snmptrap.log
Timeout=4
AlertScriptsPath=/usr/lib/zabbix/alertscripts
ExternalScripts=/usr/lib/zabbix/externalscripts
FpingLocation=/usr/bin/fping
Fping6Location=/usr/bin/fping6
LogSlowQueries=3000
StatsAllowedIP=127.0.0.1

zabbix:~# openssl version
OpenSSL 1.1.1d 10 Sep 2019