Zabbix has certificate expire date check, such date is represented in unixtime format. Sometimes expire date from far future (2038+ year) already. Currently Zabbix frontend does not show unixtime value correctly because of built-in check: https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/ui/include/func.inc.php#194
For example:

zabbix_sender -z 127.0.0.1 -s "Zabbix server" -k test -o "Mon Feb 12 15:03:55 CET 2029"

In Zabbix frontend value looks like:

Expected in Zabbix frontend and in notifications: