Incorrect output from getMonthlyBalances function calculating stock balances

I have a function called getMonthlyBalances that takes two arrays, stocks and trades, as input and calculates the monthly balance of a user's stock holdings based on their trade history. The stocks array contains objects with stock id, prices, and dates, while the trades array contains objects with stock id, quantity, price, type (buy/sell), and timestamp.

Here's the code for the function:

function getMonthlyBalances(stocks, trades) {
  if (!stocks || !trades) {
    return [];
  }

  if (trades.length === 0) {
    return {};
  }

  // Sort trades by timestamp
  trades.sort((a, b) => a.timestamp.seconds - b.timestamp.seconds);

  // Get the first trade month and create a date object
  const firstTradeDate = new Date(trades[0].timestamp.seconds * 1000);
  firstTradeDate.setDate(1); // Set the date to the first day of the month
  firstTradeDate.setHours(0, 0, 0, 0); // Set the time to midnight

  const monthlyBalances = {};
  let currentDate = firstTradeDate;

  // Initialize the user's stock holdings
  const userStocks = {};

  while (currentDate <= new Date()) {
    const currentMonth = currentDate.getMonth();
    const currentYear = currentDate.getFullYear();
    const currentMonthStr = `${currentYear}-${currentMonth + 1}`;

    trades.forEach(trade => {
      const tradeDate = new Date(trade.timestamp.seconds * 1000);
      if (tradeDate.getFullYear() === currentYear && tradeDate.getMonth() === currentMonth) {
        if (trade.type === "buy") {
          userStocks[trade.id] = (userStocks[trade.id] || 0) + trade.quantity;
        } else if (trade.type === "sell") {
          userStocks[trade.id] = (userStocks[trade.id] || 0) - trade.quantity;
        }
      }
    });

    let balance = 0;
    for (const stockId in userStocks) {
      const stock = stocks.find(stock => stock.id === parseInt(stockId));
      const stockPrice = stock.prices.find(price => {
        const priceDate = new Date(price.date.seconds * 1000);
        return priceDate.getFullYear() === currentYear && priceDate.getMonth() === currentMonth;
      });

      if (stockPrice) {
        balance += userStocks[stockId] * stockPrice.price;
      }
    }

    monthlyBalances[currentMonthStr] = balance;

    currentDate.setMonth(currentDate.getMonth() + 1);
  }

  return monthlyBalances;
}

And here are the input data examples:

// trades
[
  {
    "id": 1, // stock_1
    "quantity": 10,
    "price": 120,
    "type": "buy",
    "timestamp": {
      "seconds": 1672589479,
      "nanoseconds": 858000000
    }
  },
  {
    "id": 1, // stock_1
    "quantity": 10,
    "price": 110,
    "type": "buy",
    "timestamp": {
      "seconds": 1675354636,
      "nanoseconds": 858000000
    }
  }
]

// stocks
[
  {
    "id": 1,
    "prices": [
      {
        "price": 120,
        "date": {
          "seconds": 1678860000,
          "nanoseconds": 267000000
        }
      },
      {
        "price": 100,
        "date": {
          "seconds": 1672552800,
          "nanoseconds": 32000000
        }
      }
    ]
  },
  {
    "id": 2,
    "prices": [
      {
        "price": 120,
        "date": {
          "seconds": 1677650400,
          "nanoseconds": 12000000
        }
      },
      {
        "price": 90,
        "date": {
          "seconds": 1672552800,
          "nanoseconds": 145000000
        }
      }
    ]
  }
]

The problem is that the function produces incorrect output for certain months. For example, in February, the balance should be 1000, but the function returns 0. I can't figure out why this is happening.

Can anyone help me understand what's wrong with the function, and how to fix it to get the correct balance for each month?

Desired output:

[{2023-1: 1000, 2023-2: 1000, 2023-3: 2400}]

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