UWP Boolean not being updated in UI if set after awaited async call

I have a public boolean in my UWP app used to show/hide a ProgressBar. I've used the same pattern elsewhere and it seems to work okay, but I'm having an issue on a specific page where it doesn't seem to update in the UI only if I set the boolean after an awaited async call (same pattern as the working page).

Here is my XAML View:

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <TextBlock Text="{ x:Bind Vm.IsLoaded }" Margin="112,272,-112,-272"></TextBlock>
</Grid>

And the codebehind:

public sealed partial class MainPage : Page
{
    public MainPageViewModel Vm => DataContext as MainPageViewModel;
    public MainPage()
    {
        this.InitializeComponent();
        this.DataContext = new MainPageViewModel();
    }

    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        base.OnNavigatedTo(e);

        Vm.GetProjectData();
    }
}

Here is my MainPageViewModel.cs

public class MainPageViewModel : ViewModel
{
    public ObservableCollection<Project> Projects { get; set; } = new ObservableCollection<Project>();

    private bool _isLoaded;
    public bool IsLoaded
    {
        get { return _isLoaded; }
        set
        {
            _isLoaded = value;
            OnPropertyChanged();
        }
    }

    public async Task GetProjectData()
    {
        // If I put `IsLoaded = true;` here it displays `true` in the UI
        var projectsResponse = await HttpUtil.GetAsync(StringUtil.ProjectsUrl());
        // If I put `IsLoaded = true;` here it still displays `false` in the UI
        if (projectsResponse.IsSuccessStatusCode)
        {
            var projectsResponseString = await projectsResponse.Content.ReadAsStringAsync();
            var projects = JsonUtil.SerializeJsonToObject<List<Project>>(projectsResponseString);

            foreach (var project in projects)
            {
                Projects.Add(project);
            }

            IsLoaded = true;
       }
    }
}

And my ViewModel.cs

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

No matter where I put the IsLoaded = true; it always hits OnPropertyChanged().

Here is my working code:

ProjectViewViewModel.cs:

public class ProjectViewViewModel : ViewModel
{
    public ObservableCollection<Story> MyData { get; set; } = new ObservableCollection<Story>();
    private bool _dataIsLoaded;
    public bool DataIsLoaded
    {
        get { return _dataIsLoaded; }
        set
        {
            _dataIsLoaded = value;
            OnPropertyChanged();
        }
    }

    public async Task GetData(Project project)
    {
        DataIsLoaded = false;
        var stringResponse = await HttpUtil.GetAsync(StringUtil.Query(project.Id, "MB"));
        if (stringResponse.IsSuccessStatusCode)
        {
            // Do Stuff

            DataIsLoaded = true;
        }
    }
}

ProjectView.xaml.cs

public sealed partial class ProjectView : Page
{
    public Project Project { get; set; }
    public bool IsLoaded { get; set; }
    public ProjectViewViewModel Vm => DataContext as ProjectViewViewModel;
    public ProjectView()
    {
        this.InitializeComponent();
        this.DataContext = new ProjectViewViewModel();
    }

    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        base.OnNavigatedTo(e);

        Project = e.Parameter as Project;
        Vm.GetData(Project);
    }
}

I feel like I'm missing something extremely obvious but I can't see the wood through the trees and it's driving me nuts. Any help is greatly appreciated!