Express handler called again without client request

In the code below, the client POSTs some data to /somewhere and then the route handler callback is executed.

Inside the callback I'm waiting for a Promise to resolve before I send some result back to the client.

The Promise will take quite some time to resolve. This is expected.

I don't know how long it will take because at around 2-3 minutes into the Promise execution the app.post('/somewhere') handler is called again, even though the client makes no such request (checked). There is no activity on the client during all this time, no page refresh, redirect..nothing.

Also, no errors are thrown from forSomethingReallySlow() as nothing relevant is logged on the Node console. And I have extensive logs from within forSomethingReallySlow() where everything is working fine until the handler is called again and forSomethingReallySlow() restarts.

app.use(cors({
   origin: '*',
   credentials: true,
   optionSuccessStatus: 200
}))

app.use(function(req, res, next) {
  res.header('Access-Control-Allow-Origin', 'http://localhost:4200')
  res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept, Authorization')
  res.header('Access-Control-Allow-Methods', 'POST, GET')
  next()
})

app.use(cookieParser())
app.use(bodyParser.json({limit: "50mb"}));
app.use(bodyParser.urlencoded({limit: "50mb", extended: true, parameterLimit:50000}))
app.use(session({
  secret: 'googoogaga',
  resave: false,
  saveUninitialized: false
}))
app.use(passport.initialize())
app.use(passport.session())

passport.use(new FacebookStrategy({
  clientID      : FACEBOOK_APP_ID,
  clientSecret  : FACEBOOK_APP_SECRET,
  callbackURL   : "http://localhost:4200/facebook/callback",
  profileFields : ['id']
}, async(accessToken, refreshToken, profile, done) => {
  let facebookId = profile.id
  let userInDb =  await DB.getUser()
  if (userInDb && userInDb.facebookId === facebookId) {
    await DB.updateUser({ accessToken })
    done(null, userInDb)
  } else {
    let newUser = await DB.updateUser({ facebookId, accessToken })
    done(null, newUser)
  }
}))

passport.serializeUser(function(user, done) {
  done(null, user)
})

passport.deserializeUser(function(user, done) {
  done(null, user)
})


app.post('/somewhere', ensureLoggedIn('/auth/facebook'), jsonParser, async function(req, res){

  console.log('new POST request at: ', new Date())

  let result = await forSomethingReallySlow(req.body)

  res.status(200).send({ result })

})

Is there some internal Express feature that re-calls a handler if it takes too long to respond? And can I disable it ? Or is there something else wrong ? Thank you for your help in advance.

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