DataGrid doesnt proper loads rows

Describe the bug

Setting the DataGrid.ItemsSource to an enumerable/collection doesnt show the rows of items. Only the columns are generated, if AutoGenerateColumns has not been set to false.

Steps to Reproduce

Steps to reproduce the behavior:

Add a DataGrid to a page
Databind OR Set ItemsSource directly from code behind
Launch the app, and navigate to that page

Expected behavior

The data to be displayed.

Screenshots

n/a

Environment

NuGet Package(s):

<PackageReference Include="Uno.Microsoft.Toolkit.Uwp.UI.Controls" Version="6.1.0-build.186.g928c99f74d" />
<PackageReference Include="Uno.Microsoft.Toolkit.Uwp.UI.Controls.DataGrid" Version="6.1.0-build.186.g928c99f74d" />

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x] macOS
- [x] WASM
- [ ] iOS (?: not tested)
- [ ] Android (?: not tested)
- [ ] UWP

Visual Studio 
- [ ] 2017 (version: )
- [x] 2019 (version: ) 
- [ ] 2019 Preview (version: )

Additional context

note: If you attach the assignment to a button handler. Tapping a first time will make the columns to be generated, and tapping it again will cause the rows to be shown.

workaround:

public static class DataGridExtensions
{
    #region Property: DelayedItemsSource

    public static DependencyProperty DelayedItemsSourceProperty { get; } = DependencyProperty.RegisterAttached(
        "DelayedItemsSource",
        typeof(IEnumerable),
        typeof(DataGridExtensions),
        new PropertyMetadata(default, (d, e) => d.Maybe<DataGrid>(control => OnDelayedItemsSourceChanged(control, e))));

    public static IEnumerable GetDelayedItemsSource(DataGrid obj) => (IEnumerable)obj.GetValue(DelayedItemsSourceProperty);
    public static void SetDelayedItemsSource(DataGrid obj, IEnumerable value) => obj.SetValue(DelayedItemsSourceProperty, value);

    #endregion

    private static void OnDelayedItemsSourceChanged(DataGrid sender, DependencyPropertyChangedEventArgs e)
    {
        // DataGrid not showing rows with initial values, only "late" provided values are displayed somehow...
        // This is the workaround for that:
        _ = RunOnUIThread(() => sender.ItemsSource = (IEnumerable)e.NewValue);
    }

    private static async Task RunOnUIThread(Action action)
    {
        await CoreApplication.MainView.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
        {
            action();
        });
    }
}

for databinding, just bind to that attached property instead of ItemsSource. for code-behind, just call SetDelayedItemsSource during OnLoaded like so:

Task.Run(() => DataGridExtensions.SetDelayedItemsSource(dg, items));

unoplatform / Uno.WindowsCommunityToolkit