I'd suggest adding
**Restart=always RestartSec=10**
to /usr/share/vyos/templates/telegraf/override.conf.j2 as it is done for ntp.service.
Otherwise the telegraf service do not start - it does 5 start attempts very quickly during boot with error:
Sep 07 11:43:59 vyos-lns-1 systemd[1]: telegraf.service: Failed with result 'exit-code'. Sep 07 11:43:59 vyos-lns-1 systemd[1]: telegraf.service: Scheduled restart job, restart counter is at 5. Sep 07 11:43:59 vyos-lns-1 systemd[1]: telegraf.service: Start request repeated too quickly. Sep 07 11:43:59 vyos-lns-1 systemd[1]: telegraf.service: Failed with result 'exit-code'.
and stays in a failed state.
see boot log attached.