seems that werk #14733 does not fix the issue with systemd.
I have still the same issue with 2.1.0p25:
Apr 3 10:53:00 pi2 systemd[1]: Started Checkmk agent updater.
Apr 3 10:53:01 pi2 systemd[1]: cmk-update-agent.service: Succeeded.
Apr 3 10:54:00 pi2 systemd[1]: Started Checkmk agent updater.
Apr 3 10:54:01 pi2 systemd[1]: cmk-update-agent.service: Succeeded.
Apr 3 10:55:00 pi2 systemd[1]: Started Checkmk agent updater.
Apr 3 10:55:01 pi2 systemd[1]: cmk-update-agent.service: Succeeded.
Apr 3 10:56:00 pi2 systemd[1]: Started Checkmk agent updater.
Apr 3 10:56:01 pi2 systemd[1]: cmk-update-agent.service: Succeeded.
cat /etc/systemd/system/timers.target.wants/cmk-update-agent.timer
[Unit]
Description=Periodic Checkmk agent update
[Timer]
OnCalendar=minutely
[Install]
WantedBy=timers.target