[Bug] LinearGradientBrush doesn't fill the pages upon orientation change on iOS

[CMarcher]

Description

When I set the background of a ContentPage or NavigationPage to a LinearGradientBrush, then change the orientation of the device running the app, the background rotates as it should, but it does not redraw properly to fill the screen. When a ContentPage's background is set to a LinearGradientBrush then rotated, a white bar is visible on the edge depending on the starting orientation. Whereas when a NavigationPage's BarBackground is set to a LinearGradientBrush, the gradient appears to stack horizontally.

Steps to Reproduce

1. Create a new ContentPage or NavigationPage
2. Set the Background or BarBackground property to a LinearGradientBrush with Start/EndPoints and Offsets of your choosing.
3. Rotate the emulator / device screen.

Expected Behavior

Gradient redraws to fill the screen properly.

Actual Behavior

Gradient rotates but doesn't fill screen, either leaving a white bar or another gradient stacks horizontally on it. NavigationPage gradient doesn't seem to have issues on a 13.6 device, but still white bar for ContentPage.

Basic Information

• Version with issue:

• Last known good version: None, issue ever since the experimental version released with Xamarin Forms 4.8.

• IDE: Visual Studio 2019, version 16.7

• Platform Target Frameworks:

  • iOS: 13.6, though screenshots on physical device on 12.4.5.

• Nuget Packages:

  • EntityFramework (6.4.4),
  • NetStandard.Library (2.0.3),
  • sqlite-net-pcl (1.7.335),
  • Syncfusion.Licensing (18.2.0.48),
  • Syncfusion.Xamarin.Buttons (18.2.0.48),
  • Syncfusion.Core (18.2.0.48),
  • Syncfusion.Xamarin.SfChart (18.2.0.48),
  • Syncfusion.Xamarin.SfListView (18.2.0.48),
  • Syncfusion.Xamarin.SfTabView (18.2.0.48),
  • Xamarin.Essentials (1.5.3.2),
  • Xamarin Forms (4.8.0.1269)

• Affected Devices:
  Phone and Tablet.

Screenshots

Workaround

You can set the Background property of a StackLayout, AbsoluteLayout, etc. that fills the screen, will redraw properly. Can't find workaround for NavigationPage.BarBackground, apart from not setting Background entirely and using a custom renderer instead.