UIKit Consistency error: you are calling a UIKit method in Xamarin iOS

Question

I build Chat application in Xamarin combined with Firebase Realtime Database. I test the app on Android emulator, it works fine. However when I run the Xamarin iOS app, I test it very slowly, on average it takes about 25-30s to display the message content. And after that I get the error: UIKit.UIKitThreadAccessException: 'UIKit Consistency error: you are calling a UIKit method that can only be invoked from the UI thread.'.I have consulted the articles here, but I still can't solve the problem

public ObservableCollection<MyDatabaseRecord> DatabaseItems { get; set; } = new ObservableCollection<MyDatabaseRecord>();
public static string FirebaseClient = "https://xxxxxxxxxxxxxxxxxxxxxxxxx.firebasedatabase.app/";
public static string FrebaseSecret = "PzxmWhdeDb7WM1JQmxxxxxxxxxxxxxxxxxxxxx";
public FirebaseClient fc = new FirebaseClient(FirebaseClient,
                   new FirebaseOptions { AuthTokenAsyncFactory = () => Task.FromResult(FrebaseSecret) });
public string roomid { get; set; }
public DetailChats(string roomID)
{
    InitializeComponent();
    roomid = roomID;
    LoadChat();
}

protected async void LoadChat()
{
    if (roomid != "")
    {
        string nameroom = "";

        BindingContext = this;
        string userget = "12345678";

        Device.BeginInvokeOnMainThread(() =>
        {
            var FirebaseClient = fc
            .Child("RecordsChat").Child(roomid)
            .AsObservable<MyDatabaseRecord>()
            .Subscribe(async (dbevent) =>
            {
                if (dbevent.Object != null)
                {
                    if (dbevent.Object.sender_uid == userget || dbevent.Object.receiver_uid == userget)
                    {
                        dbevent.Object.BackgroundUser = "#2085d000";
                    }
                    else
                    {
                        dbevent.Object.BackgroundUser = "#fafafa";
                    }

                    DatabaseItems.Add(dbevent.Object);

                    if (dbevent.Object.receiver_uid == userget)
                    {
                        await UpdateStatus(false, true);

                        nameroom = dbevent.Object.sender_uid;
                    }
                    else
                    {
                        nameroom = dbevent.Object.receiver_uid;
                    }

                    var customerList = await apiServiceUserinfo.GetCustomersInfo(nameroom);
                    string nameget = customerList.NameStore;

                    title_chat.Text = nameget;
                }
                else
                {
                    string namestore = Preferences.Get("GetNameStoreChat", "namestore");

                    nameroom = namestore;

                    var customerList = await apiServiceUserinfo.GetCustomersInfo(nameroom);
                    string nameget = customerList.NameStore;

                    title_chat.Text = nameget;
                }
            });
        });
    }   
}

How can I solve the problem:

1. Improved display of data content from Firebase Realtime Database. Where did I go wrong?
2. Error: UIKit.UIKitThreadAccessException: 'UIKit Consistency error: you are calling a UIKit method that can only be invoked from the UI thread.'

Thanks for all the results