session can't be accessed because req.sessionID keeps changing on each request

Question

I am trying to access req.sessionID in express-session and connect-mongo so that I can access the session in my MongoStore. However, despite the cookie being the same in Chrome Dev Tools as well as within the sessions db, for some reason I cannot get the correct sessionID from the request object.

I have set up a console.log within that endpoint to see req.sessionID, and every time I refresh the page to request from that endpoint, I get a different sessionID.

Here are all the parts of my code that I think might be relevant:

// Part of backend server setup

app.use(cors(
    { 
        origin: true, 
        credentials: true, 
        preflightContinue: true,
        methods: ["GET", "PATCH", "POST", "DELETE"],
        allowedHeaders: ["Access-Control-Allow-Headers"],
        optionsSuccessStatus: 200,
    }
));

app.use((req, res, next) => {
    res.setHeader("Access-Control-Allow-Origin", "https://localhost:3000");
    res.setHeader("Access-Control-Allow-Credentials", true);
    res.header("Access-Control-Allow-Origin", "https://localhost:3000");
    res.header("Access-Control-Allow-Credentials", true);
    res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
    res.header(
      "Access-Control-Allow-Headers",
      "Origin, X-Requested-With, Content-Type, Accept, Cookie, Credentials"
    );
    next();
});

app.use(Session({
    name: 'auth-cookie',
    secret: process.env.SESSION_SECRET,
    resave: false,
    saveUninitialized: false,
    store: MongoStore.create({
        mongoUrl: process.env.MONGODB_URI,
        dbName: dbName,
        collectionName: collectionName,
        clientPromise: clientP,
        autoRemove: 'native',
        autoRemoveInterval: 15,
        ttl: 14 * 24 * 60 * 60,
        serialize: function (obj) {
            return new Object(obj);
        },
    }),
    cookie: {
        sameSite: 'none',
        secure: true, 
        httpOnly: true,
        maxAge: 14 * 24 * 60 * 60,
    },
}));

// Part of frontend server setup

app.prepare().then(() => {
  https.createServer(options, async (req, res) => {
      res.setHeader("Access-Control-Allow-Origin", "https://localhost:8080");
      res.setHeader("Access-Control-Allow-Credentials", true);
      res.setHeader('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
      res.setHeader(
        "Access-Control-Allow-Headers",
        "Origin, X-Requested-With, Content-Type, Accept, Cookie, Credentials"
      );

      let urlStr;
      if (req.url.includes('localhost')) {
        urlStr = '';
      } else {
        urlStr = req.url;
      }

      const parsedUrl = new URL(urlStr, "https://localhost");
      await handle(req, res);

  }).listen(port, (error) => {
      if (error) throw error;
      console.log(`> Ready on https://${hostname}:${port}`)
  })
})

// Frontend request to backend

async function getUser() {
    const res = await fetch("https://localhost:8080/user", {
        credentials: "include",
        headers: {"credentials": "include"},
        method: 'GET',
    })
  .then(res => res.json())
}

I've looked at several other similar posts, and still can't find a solution. If anyone knows what might be missing, please let me know as well.

Thank you.

Edit: The frontend node HTTPS server seems to have access to sessionID. Any way to get it over to the backend HTTPS server?

Edit_2: I've made another observation, that the cookie is actually available on both frontend and backend servers, and that fetching a user isn't a problem at all. for some reason the data just isn't being sent over properly. It keeps giving me a status 400 code on the frontend server, even though I can see the found user on the backend server.

Edit_3: I noticed that when I request the user directly from the backend server, I get data back without any issues. However, when I request the user from the frontend using fetch, I get null back. Does anyone know what might be causing this?

Here is what I have for the get request for sending the user data over to frontend:

    ...

    const user = await User.findOne({ _id: new ObjectId(req.session['userId']) })
    
    if (user === null) {
        return res.status(400).send({ message: "Authentication Failed" });
    }

    return res.status(201).json(user);
});