requestSingleInstanceLock always returns true on Windows 10

Electron 4.1.0
Windows 10 professional
Our application is started by invoking a register URL.
I am never seeing the requestSingleInstanceLock return false.
I am never seeing the second-instance event.

const gotTheLock = app.requestSingleInstanceLock();

if (!gotTheLock) {
  log.info(`Not the first instance - quit`);
  app.quit();
  return;
}

log.info('Got the single instance lock');

app.on('second-instance', (event, commandLine, workingDirectory) => {
  log.info(`second-instance ${commandLine} ${workingDirectory}`);
  rewritePortFile();
});

Does the single instance code rely on having a renderer window open/created?
Because our application does post-processing on user data, with no window
and can be invoked for another task during that time?