nodejs express server stops unexpectedly - node.js

Question

I have a server built with express and socket IO. The problem is that every time the server just stops responding 2 minutes after first client connection. Things I have already done/checked:
Express logs show no errors.
socket.IO logs show no errors on server side.
socket.IO logs show ping timeout on client side (after a few successful pings).
Listening to the uncaughtException/UnhandeledRejection doesn't help.
So, when I start the server, and GET /login through the browser, without doing anything else, the server will stop responding on its own after ~2 minutes, and the only way to close it is closing the cmd (CTRL+C doesn't work even after listening to SIGINT).
I'll post the relevant parts of the code here:
server.js
const http = require('http');
const express = require('express');
const socketIO = require('socket.io');
let app = express();
let server = http.createServer(app);
var io = socketIO(server);
app.get(`/login`, (req, res) => {
console.log(`got GET /login`);
res.sendFile(publicPath + '/login.html');
});
io.on(`connection`, (socket) => {
socket.on(`login`, async (details, cb) => {
login(details.username, details.password, async (res) => {
if (res === true) {
let user = new User(details.username, details.password);
let token = await user.generateAuthToken();
cb(`/set?token=${token}`);
} else if (res === false) {
socket.emit(`loginFailed`, 'Password incorrect. Please try again!')
} else if (res === `Username doesn't exist`) {
socket.emit(`loginFailed`, res)
}
});
});
socket.on('getAllLeads', async (callback) => {
leads = await getAllLeads();
callback(leads);
});
socket.on('getSomeLeads', async (options, callback) => {
leads = await getSomeLeads(options);
callback(leads);
});
socket.on(`newFile`, ({text, words, options, fileName}) => {
console.log('Starting...');
words.forEach((wordSet, index) => {
wordSet.forEach(word => {
regexp = `\\s+${word}+\\s`;
re = new RegExp(regexp);
text = text.replace(re, `${options[index]}`);
});
});
fs.writeFileSync(`${fileName}.txt`, text, 'utf8');
console.log(`Finished writing to ${fileName}.txt successfully!`);
});
});
server.listen(3000, () => {
console.log(chalk.yellow(`Server is up on port ${port}`));
});
login.js
const socket = io();
socket.on(`reconnect_error`, (err) => {
console.log(err);
});
socket.on(`connect`, () => {
console.log('connected to login page');
if (getQueryVariable('failed')) {
$('.error, .error p').css('opacity', 1);
$('.error p').text('Unauthorized! PLEASE log in.');
}
socket.on(`loginFailed`, (reason) => {
$('.error, .error p').css('opacity', 1);
$('.error p').text(reason);
console.log(`got login failed`);
});
$('#form').submit((e) => {
e.preventDefault();
let username = $('#username').val();
let password = $('#pass').val();
socket.emit(`login`, {username, password}, (path) => {
window.location.href = path;
});
});
});
function getQueryVariable(variable)
{
var query = window.location.search.substring(1);
var vars = query.split("&");
for (var i=0;i<vars.length;i++) {
var pair = vars[i].split("=");
if (pair[0] == variable) return pair[1];
}
return (false);
}