Why do I get NaN value in react?

Whilst I am doing cart in react, I have no idea why I keep getting NaN value – only from a specific object data.

When I have the following data list:

export const ItemsList = [
  {
    id: 1,
    name: "VA-11 Hall-A: Cyberpunk Bartender Action",
    price: 110000,
    image: cover1,
    link: "https://store.steampowered.com/app/447530/VA11_HallA_Cyberpunk_Bartender_Action/?l=koreana",
  },
...
  {
    id: 6,
    name: "Limbus Company",
    price: 110000,
    image: cover6,
    link: "https://limbuscompany.com/",
  },
];

And the following code, please look at the comment line.

import React, { useContext } from "react";
import "./Goods.css";
import { DataContext } from "../../components/context/DataContext";

export const Goods = (props) => {
  const { id, name, price, image, link } = props.shopItemProps;
  const { cartItems, addItemToCart, removeItemFromCart } =
    useContext(DataContext);
  const cartItemStored = cartItems[id];

  return (
    <div className="goods">
      <div className="goods-id">{id}</div>
      <img src={image} alt="thumbnail_image" className="goods-image" />
      <div className="goods-name">{name}</div>
      <div className="goods-price">${price}</div>
      <button>
        <a href={link} className="goods-link">
          Official Store Page
        </a>
      </button>
      <div className="cart-button">
        <button onClick={() => removeItemFromCart(id)}>-</button>
// ★Maybe here? but why do I get NaN only for id:6? Others work well.
        {cartItemStored > -1 && <> ({cartItemStored}) </>}
        <button onClick={() => addItemToCart(id)}>+</button>
      </div>
    </div>
  );
};

What should I do to solve NaN? There seems to be no way to make that value as int in this case. Or do you see any problem from the above code block?

Thanks.