{"fatal":true} error on deployed heroku backend nodejs server

I am getting error code 400 when I try to login through my frontend. When I see my heroku logs I think it send the query to the database but doesn't gets the result back instead gets an error.

This only happens when the server is running for quite a time and is resolved if I just restart the heroku server.

Code for my login endpoint is:

const Login = (req, res) => {
  if (!req.session.user) {
    try {
      const user = req.body;
      let sql = `SELECT * FROM users WHERE type_id=?;`;
      db.query(sql, user.type_id, async (err, result) => {
        if (err) res.status(400).send(err);
        if (result[0]) {
          if (await argon2.verify(result[0].password, user.password)) {
            req.session.user = {
              type: result[0].type,
              id: result[0].UserId,
              name: result[0].full_name,
              typeId: result[0].type_id,
            };
            res.status(200).send("logged in");
          } else res.send("wrong password");
        } else res.send("invalid id / user doesnot exist sign up first");
      });
    } catch {
      res.status(500).send(null);
    }
  } else res.send("already logged in");
};

This happens for my root endpoint also :

app.get("/", (req, res) => {
  try {
    const sql = "SELECT * FROM users;";
    db.query(sql, (err, result) => {
      if (err) res.send(err);
      res.send(result);
    });
    console.log(req.session);
  } catch {
    res.status(500).send(null);
  }
});

Here when I go to the root from my browser it shows

{"fatal":true}

Again from the heroku logs all I can make out of it is that whenever the query is sent to the database it send back error.