systemd stops restarting service

StartLimitIntervalSec= belongs to the [Unit] section. See https://www.freedesktop.org/software/systemd/man/systemd.unit.html#

[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. ...

Like this:

[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