How to solve threading problem in WPF? Using MVVM

Question

I write an application using MVVM pattern. My main view model have a property 'CurrentViewModel'. When I click top panel buttons (Account, Trade History etc...) CurrentViewModel property is updated. SpotViewModel is constantly getting the candles info from Binance api and updating UI in async method GetChartDataAsync() and everything works fine. But when I click any top panel button, for example Trade History, I get an exception "object reference not set to an instance of an object". Help please.

Here is The UI:

Spot View

Here is SpotViewModel constructor. It is called when I click 'Spot' button and it assigns the SpotViewModel to the CurrentViewModel property:

public SpotViewModel(List<UserLoginInfo> appUsers, string selectedExchange)
{
    SelectedExchange = selectedExchange;
    ExchangeUsers = appUsers;

    foreach (var user in ExchangeUsers)
    {
        AvailableExchanges.Add(user.Exchange);
    }

    Symbol24Stats.Symbol = "XRPUSDT";
}

Here is GetChartDataAsync method:

public async Task GetChartDataAsync(CancellationToken token)
{
    TimeFrame timeFrame = FancyCandles.TimeFrame.M5;
    CandlesSource candles = new CandlesSource(timeFrame);

    while (true)
    {
        if (token.IsCancellationRequested)
        {
            return;
        }
        List<TradingCommonTypes.ICandle> exchangeCandles = new List<TradingCommonTypes.ICandle>();

        try
        {
            exchangeCandles = AppUser.MarketInfo.GetCandles(Symbol24Stats.Symbol, "5m", 500);
        }

        catch { continue; }

        Application.Current.Dispatcher.Invoke(() =>
        {
            candles.Clear();
            foreach (var candle in exchangeCandles)
            {
                candles.Add(new Candle(candle.OpenTime, candle.Open, candle.High, candle.Low, candle.Close, candle.Volume));
            }
        });

        SpotCandles = candles;                
    }
}

Here is The command from MainViewModel which assigns the CurrentViewModel property:

public void OnSelectMainMenuTabCommandExecuted(object p)
{
    var activeTabColor = new SolidColorBrush((Color)ColorConverter.ConvertFromString("#D81D3C"));

    switch (p as string)
    {
        case "Account":
            accountBackgroundWorker.DoWork += AccountBackgroundWorker_DoWork;
            accountBackgroundWorker.RunWorkerCompleted += AccountBackgroundWorker_RunWorkerCompleted;
            accountBackgroundWorker.RunWorkerAsync();
            break;
        case "History":
            cts.Cancel();

            tradeHistoryBackgroundWorker.DoWork += TradeHistoryBackgroundWorker_DoWork;
            tradeHistoryBackgroundWorker.RunWorkerCompleted += TradeHistoryBackgroundWorker_RunWorkerCompleted;
            tradeHistoryBackgroundWorker.RunWorkerAsync();
            break;
        case "Spot":
            tradeHistoryBackgroundWorker.DoWork += SpotBackgroundWorker_DoWork;
            tradeHistoryBackgroundWorker.RunWorkerCompleted += SpotBackgroundWorker_RunWorkerCompleted;
            tradeHistoryBackgroundWorker.RunWorkerAsync();
            break;
        case "Auto":
            AutoTradingTabBackground = activeTabColor;
            break;
        case "Futures":
            FuturesTabBackground = activeTabColor;
            break;
    }

    MainMenuSpinnerVisibility = Visibility.Visible;
    IsExchangeSelectionEnabled = false;
}

Calling of async task is happening in SpotBackgroundWorker_RunWorkerCompleted:

private void SpotBackgroundWorker_RunWorkerCompleted(object? sender, RunWorkerCompletedEventArgs e)
{
    SetMainTabsBackgroundToDefault();
    SpotTabBackground = new SolidColorBrush((Color)ColorConverter.ConvertFromString("#D81D3C"));
    MainMenuSpinnerVisibility = Visibility.Collapsed;
    IsExchangeSelectionEnabled = true;

    Task.Run(() => ((SpotViewModel)CurrentViewModel).GetChartDataAsync(cts.Token));

}