Collection not populating except when stepping through the code.

Thank you, Amit, for your reply. Yes, the code is incomplete in so far as it is only four methods out of several classes and a lot more methods. I included the methods that make up the view that is the problem. If async await does not wait for the method to complete, then what does? The only thing I can think of now is to add a lot of pauses throughout to slow it all down. This is only a problem when the program starts. Once the collection is populated, there is no need to run through this again. I can say without a doubt it is an asyncronous issue. It ran perfectly twice at full speed. 

I must not yet understand async await. Nothing is "awaited" the code just runs on and leaves the result of the called method hanging. When wathcing the threads, one will show the thread created with the call to GetInstrumentPortsAsync. Within that there is a call to GetInstrumentIDAsync. That method actually queries the instrument for it's ID. I have awaited that one too.At the moment my code looks like this:

public  Instruments
{
    get => instruments;
    set
    {
        instruments=value;
        RaisePropertyChanged();
    }

}

Public MainWindowViewModel()
{
	LoadInstruments();
}

public async void LoadInstruments
{
    InstrumentComs? ic = new();
    InstrumentCollection = await Task.Run(()=>ic.GetInstrumentPortsAsync());
    if (InstrumentCollection == null)
    {
        //Do something
    }
}

ic Class

public async Task> GetInstrumentPortsAsync();
{
    ObservableCollection ports = new();
    foreach (string port in SerialPort.GetPortNames())
    {
        SerialPort sp = new()
        {
            PortName = port,
            ReadBufferSize = 1024,
            DiscardNull = true,
            RtsEnable = true,
            DtrEnable = true,
            ReceivedBytesThreshold = 1,
            BaudRate = 9600,
            StopBits = StopBits.One,
            Parity = Parity.None,
            DataBits = 8
        };

        try
        {
            sp.Open();
            if (sp.IsOpen)
            {
                string instID = await GetInstrumentId(sp);  
                if (instID != null)
                {
                    if (instID.ToString().Contains("InstNo"))
                    {
                        InstrumentViewModel ivm = new();
                        ivm.Parity = sp.Parity;
                        ivm.StopBits = sp.StopBits;
                        ivm.InstID = instID.ToString().Split(',').ElementAt(2);
                        ivm.BaudRate = sp.BaudRate;
                        ivm.PortName = sp.PortName;
                        ivm.DataBits = 8;
                        ivm.RTSEnabled = sp.RtsEnable;
                        ivm.DTREnabled = sp.DtrEnable;
                        ivm.Port = sp;
                        ivm.IsConnected = true;
                        ports.Add(ivm);
                    }
                }
            }
        }
        catch (InvalidOperationException)
        {
           //Handle it
        }
    }
    return ports;
}


public Task GetInstrumentID(string port)
{
  try
    {
        string response = string.Empty;
        sp.WriteLine("*IDN?");
        while (sp.BytesToRead > 0)
        {
            respose += sp.ReadExisting();
        }
        return response.Replace("\r", "").Trim(); 
}

What can I do differently?

I think the issue you're encountering is likely due to the asynchronous nature of your code and how you're handling the task results in the view model's constructor. When you step through the code, it gives time for the asynchronous operations to complete, but when running normally, the operations don't complete before the constructor finishes executing. So you need to ensure that your view model correctly waits for the asynchronous operation to complete before checking the result.

Also your code appears to be incomplete or incorrectly provided.