Steps to reproduce:

1. Set up postgresql plus pgboucer as reverse proxy for zabbix-server
2. Set up zabbix server (PG build) from official repo, point to pgbouncer as DB host
3. Start up postgresql, pgbouncer, zabbix-server
4. systemctl stop pgbouncer
5. systemctl stop zabbix-server

Result:
Zabbix server cannot stop forever complaining that DB is down (see screenshot). So, during machine reboot zabbix stopping will run forever, preventing whole server from normal rebooting.

Expected:
Zabbix server WILL stop after some time if SIGTERM received AND DB is unreachable.

Also, it is expected to have:

[Unit]
After=pgbouncer.service
After=postgresql-9.4.service
After=postgresql-9.5.service
After=postgresql-9.6.service
After=postgresql-10.service
After=postgresql-11.service
After=postgresql-12.service

in /usr/lib/systemd/system/zabbix-server.service (to properly ordering zabbix-server and PGDG official builds shutdown sequence).