Including MQTT in electron application blocks `.openDevTools`

I have quite strange problem.

I'm developing electron application.

Lets focus only on main.js - it has all the basic components and then I have setupMQTT() function which handles all the MQTT stuff. So my main.js looks something like this. For the sake of simplicity I will omit a few things.

const { app, BrowserWindow } = require("electron");
const path = require("path");
const url = require("url");

import { connect, MqttClient } from "mqtt" // << this is for MQTT

// .. omitting

let MQTT: MqttClient;
function createWindow() {
  let win = new BrowserWindow(/* ..omitting.. */);

  win.loadURL(/* ..omitting.. */);

  win.webContents.openDevTools({ mode: 'detach' });

  win.on("closed", () => {
    win = null;
  });
}

// .. omitting

app.on("ready", () => {
  createWindow();
  setupMQTT(); // << if I comment this out `....openDevTools` works
});


function setupMQTT() {
  MQTT = connect('...', {
    hostname: '...',
    port: 8883,
    protocol: 'mqtts'
  });

  MQTT.on('connect', () => {});

  MQTT.on('message', (topic, value) => {});

  MQTT.on('error', (error) => {});
}

So if I comment out setupMQTT() dev tools will show, otherwise dev tools will not (also invoking them from menu doesn't work)

note - MQTT works (I get messages and all)

Any ideas? Thanks!