Windows 10 KB4601554 is rolling out now. This same version of Windows 10 is rolling out to .Net Framework 3.5 and 4.8 Windows 10 version 2004, Windows Server version 2004, Windows 10 version 20H2, Windows Server version 20H2, and Windows Server 21H1.

This May 11, 2021 update for Windows 10 brings several reliability improvements for .NET Framework 3.5 and 4.8. All improvements are listed below and sources directly from Microsoft.

Windows 10 KB4601554

The following quality and reliability improvements available in version KB4601554:

Common Language Runtime:

  • Addresses an issue where the entire process would be torn down when a NullReferenceException propagated out of an exception filter.
  • Addresses an issue with slowdowns that could occur when making large numbers of devirtualized calls into MarshalByRefObject-derived code.

Windows Presentation Foundation::

  • Addresses an issue with lag responding to typing in TextBox, when spell-checking is enabled that was introduced in an update earlier this year.
  • Addresses an issue with a leak of touch-related resources, including OS handles, when closing a window. The leak only occurs when a touch device is active, and only for windows whose HwndSource is created directly by the app.
  • Addresses a crash when docking a window within Visual Studio, or, more generally, disposing an HwndSource whose RootVisual is null.


  • Addresses an issue in ComboBox drop down item bounding rectangle as exposed to the accessibility tools, where we did not take into account that some items might be scrolled out of view, we had always started counting items from the first visible one, and thus item rectangle location was incorrect.
  • Implemented ScrollItemPattern (IScrollItemProvider (uiautomationcore.h) – Win32 apps | Microsoft Docs) for ComboBox drop down items.

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