Electron app doesn't return when run via Windows cmd.exe

If I run my Electron exe within Command Prompt, the app is run, but when the window is closed control is not passed back to Command Prompt.

I have to Ctrl+C and then I get control back.

To intercept the closing of the window I do:

app.on('window-all-closed', () => {
    log.debug('window-all-closed' + os.EOL);
    expectKill=true;
    if (serverProcess) {
        log.debug('Killing ' + serverProcess.pid + os.EOL);
        const kill = require('tree-kill');
        kill(serverProcess.pid, 'SIGTERM', function () {
            serverProcess = null;
        });
    }
    if (process.platform !== 'darwin') {
        log.debug('app.quit()' + os.EOL);
        app.quit();
    }
    return;
})

serverProcess is a spawned process. I can see this is correctly killed.

In the logs I can see:

app.quit()

All of the processes created by the Electron app, including the serverProcess mentioned above and the Electron exe itself disappear from Task Manager.

However, control never comes back:

C:\Program Files\electron-app\bin>electron-app.exe

C:\Program Files\electron-app\bin>
19:15:06.566 > window-all-closed

19:15:06.575 > Killing 3144

19:15:06.589 > app.quit()

Sometimes, if I then restart the app, I get an odd hang:

C:\Program Files\electron-app\bin>electron-app.exe

C:\Program Files\electron-app\bin>

... the app is hung at this point and I have to Ctrl+C to get it back to cmd.exe control.

Why isn't control given back to cmd.exe after app.quit() has been called?