Broken iOS Layout with Grouped ListView

I've got a list view that looks pretty normal on Android, but on iOS, I get the category names twice. Once where they belong, and once squished over on the side.

This is the ListView XAML

    <ListView x:Name="MediaList"
              ItemsSource="{Binding MediaSections}"
              IsGroupingEnabled="True"
              GroupDisplayBinding="SectionName"
              GroupShortNameBinding="SectionName">
        <ListView.GroupHeaderTemplate>
            <DataTemplate>
                <ViewCell>
                  <StackLayout VerticalOptions="CenterAndExpand">
                    <Label Text="{Binding SectionName, Converter={StaticResource UppercaseValueConverter}}" />
                  </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.GroupHeaderTemplate>
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextCell Text="{Binding Title}" />
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

And this is the relevant CodeBehind

    // constructed once when the first module is loaded.
    // then the watcher will updated everything after the fact.
    public ModuleMediaTab()
    {
        ViewModel = new MediaPageViewModel { IsBusy = true };
        InitializeComponent();

        var subscriber = new ModuleSubscription();
        WatchForViewModelUpdates(subscriber);
    }

    // constructed each time a segment is loaded
    public ModuleMediaTab(Guid moduleId, string moduleTitle)
    {
        _moduleTitle = moduleTitle;
        ViewModel = new MediaPageViewModel { IsBusy = true };
        InitializeComponent();

        FetchMediaListAsync(moduleId);
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        BindingContext = ViewModel;
        ((ListView) MediaList).ItemTapped += (sender, args) => TriggerMedia((MediaViewModel)args.Item);
    }

    private void WatchForViewModelUpdates(ModuleSubscription subscriber)
    {
        MessagingCenter.Subscribe<MainMenu, ModulePageViewModel>(subscriber, "CurrentModuleMessage", (s, e) => Task.Run(() =>
        {
            subscriber.CurrentModule = e;
            _moduleTitle = e.Title; // this property only updates when switching modules
            FetchMediaListAsync(e.Id);
        }));
    }

    private async void FetchMediaListAsync(Guid moduleId)
    {
        await Task.Run(() =>
         {
             var mediaService = App.Container.Resolve<IMediaService>();
             var media =mediaService.FindModuleMediaByModuleId(moduleId);
             ViewModel.Media = media;
             ViewModel.IsBusy = false;
         });
    }