[Bug] [iOS] CollectionView Header will be scrolled out of view if HttpClient is used

Description

CollectionView Header will be scrolled out of view if HttpClient is used.

Updated: Seems any async call could impact the Header. The following line of code in GetItemsAsync can also make the collection view header be scroll out of view. await Task.Delay(200).ConfigureAwait(false);

Steps to Reproduce

Create a Mobile App Xamarin project.
Add header to the collection view in ItemsPage.xaml

        <CollectionView.Header>
            <StackLayout BackgroundColor="Blue">
                <Label Text="I'm in header" TextColor="White"></Label>
                <Label Text="I'm in header, too" TextColor="White"></Label>
            </StackLayout>
        </CollectionView.Header>

Use HttpClient in MockDataStore.cs public async Task<IEnumerable> GetItemsAsync(bool forceRefresh = false) { // If comment the following line, the header shows without issues. var dummyHtml = await new HttpClient().GetStringAsync("https://www.bing.com").ConfigureAwait(false); return await Task.FromResult(items); }

Expected Behavior

The header shows on top of the view.

Actual Behavior

The header is scrolled out of view and it's invisible.

Basic Information

Version with issue: 5.0.0.2196
Last known good version: N/A
Platform Target Frameworks:
- iOS:
- Android:
- UWP:
Android Support Library / AndroidX Version:
NuGet Packages: Xamarin.Essentials(1.7.0), Xamarin.Forms(5.0.0.2196)
Affected Devices: iOS

Environment

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