StartLimitIntervalSec=
pertence à seção [Unidade]. Consulte o link
[Unit] Section Options
StartLimitIntervalSec=, StartLimitBurst=
Configure unit start rate limiting. By default, units which are started more than 5 times within 10 seconds are not permitted to start any more times until the 10 second interval ends. ...
Assim:
[Unit]
StartLimitIntervalSec=0
[Service]
Restart=always
RestartSec=2
ExecStart=/usr/local/bin/node --max-old-space-size=4096 /home/somewhere/something.js
StandardOutput=null
StandardError=null
KillMode=process
[Install]
WantedBy=multi-user.target