vector doesn't work in lambda with data binding

I have a TreeView XAML control. I am data binding it to a Vector with a property:

    property Windows::Foundation::Collections::IObservableVector<TreeViewData^>^ Items
    {
        Windows::Foundation::Collections::IObservableVector<TreeViewData^>^ get() { return _containerItems; }
    }

If I append to the vector out of the lambda for my async op, it is fine. If I append in the lambda, I get this error:

Exception thrown at 0x00007FF8E8845419 in DevicePanels.exe: Microsoft C++ exception: Platform::InvalidCastException ^ at memory location 0x0000001011AFE5A0. HRESULT:0x80004002 No such interface supported WinRT information: No such interface supported

// this works       
_containerItems->Append(ref new TreeViewData());
_handlerAdded = ref new TypedEventHandler<DeviceWatcher^, DeviceInformation^>(
    [this](DeviceWatcher^ sender, DeviceInformation^ deviceInfo)
{
    Dispatcher->RunAsync(CoreDispatcherPriority::Low, ref new DispatchedHandler(
        [this, deviceInfo]()
    {   
        // this does not work
        _containerItems->Append(ref new TreeViewData(deviceInfo));

It seems like the main difference would be related to what thread the append is running on, but the error code is E_NOINTERFACE

Any suggestion?