OnNotifyPropertyChanged only triggers on the firts obj of the List

Question

I have a ParentObj" Country " which has a List child Obj "Cities". I coded a OnNotifyPropertyChanged in the child object that notifies the Parent about its changes. If I change the first obj of the child list it works! But if I change the second one, it does not trigger the event.

public abstract class AbstractInvestor : IInvestor, INotifyPropertyChanged
    { 
        private string name;
        private Stock stock;
        public abstract event PropertyChangedEventHandler PropertyChanged;
        protected int wealth;
        public abstract int Wealth //this is child property
        {
            get;
            set;
            
        }
        protected abstract void OnNotifyPropertyChanged(string propertyName);
        
        public AbstractInvestor(string name)
        {
            this.name = name;   
        }
        public void Update(Stock stock)
        {
            Console.WriteLine("Notified {0} of {1}'s " +
                "change to {2:C}", name, stock.Symbol, stock.Price);
        }
        // Gets or sets the stock
        public Stock Stock
        {
            get { return stock; }
            set { stock = value; }
        }
    }
    public  class Investor: AbstractInvestor
    {
        public override event PropertyChangedEventHandler PropertyChanged;

        public Investor(string name) : base(name)
        {

        }
        public override int Investment //this is child property
        {
            get { return investment; }
            set
            {
                if (investment!= value)
                {
                    OnNotifyPropertyChanged(value.ToString());
                    wealth = value;
                }
            }
        }
        protected override void OnNotifyPropertyChanged(string propertyName)
        {
            var tmp = PropertyChanged;
            if (tmp != null)
            {
                tmp(this, new PropertyChangedEventArgs(propertyName));
            }
        }

    } 
 public abstract class Stock 
    {
        private string symbol;
        private double price;
        public List<IInvestor> investors = new List<IInvestor>();
        
        public int MarketCap { get; set; }       

        public Stock(string symbol, double price)
        {
            this.symbol = symbol;
            this.price = price;
        }
        private void MarketCapChanged(object o, PropertyChangedEventArgs e)
        {
            int valore = int.Parse(e.PropertyName);
            if (valore!= MarketCap) 
            {
                this.MarketCap += valore;
                Console.WriteLine($"Maket value now is:{this.MarketCap}");
            } 
        }
        public void Attach(IInvestor investor)
        {
            var ivs = (Investor) investor;
            ivs.PropertyChanged += MarketCapChanged;
            investors.Add(ivs);
        }
        public void Detach(IInvestor investor)
        {
            investors.Remove(investor);
        }
        public void Notify()
        {
            foreach (IInvestor investor in investors)
            {
                investor.Update(this);
            }
            Console.WriteLine("");
        }
        // Gets or sets the price
        public double Price
        {
            get { return price; }
            set
            {
                if (price != value)
                {
                    price = value;
                    Notify();
                }
            }
        }
        // Gets the symbol
        public string Symbol
        {
            get { return symbol; }
        }
    }




static void Main(string[] args)
        {
            IBM ibm = new IBM("IBM", 120.00);
            ibm.Attach(new Investor("Sorros"));
            ibm.Attach(new Investor("Berkshire"));
            ibm.investors[0].Wealth = 1000;
            ibm.investors[1].Wealth = 1000;
            //// Fluctuating prices will notify investors
            //ibm.Price = 120.10;
            //ibm.Price = 121.00;
            //ibm.Price = 120.50;
            //ibm.Price = 120.75;
            // Wait for user
            Console.ReadKey();
        }