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Microsoft released the optional updates KB4571748 and KB4566116 for Windows 10 versions 1809, 1903 and 1909 on August 20, 2020.

The preview updates are non-security in nature and designed for testing purposes (both for administrators but also Microsoft who collects Telemetry data). Most users should wait for the official release of these updates on the September 2020 Patch Tuesday.

Microsoft did add support for WSL 2 in Windows 10 version 1903 and 1909 in this release.
It is best not to install these updates on production machines, and to create system backups before the updates are installed.

Note that the updates are listed under optional updates in the Windows 10 Settings app under Update & Security > Windows Update.

The preview update for Windows 10 version 2004 is expected to be released next week.

KB4571748 for Windows 10 version 1809 and Windows Server 2019

• Support page: KB4571748
  
• Microsoft Update Catalog: link
  

Fixes and changes

• Fixes a black screen issue in Windows Virtual Desktop during sign-in.
  
• Fixed an issue with the GetConsoleWindow function.
  
• Fixed a memory leak issue in Dynamic Data Exchange.
  
• Fixed an issue that caused touchscreens to stop working after several sleep and wake cycles.
  
• Fixed a child window flickering issue on server devices with stark visual contrasts.
  
• Fixed a preview issue of .msg files in File Explorer.
  
• Fixed an issue that caused all open UWP apps to close unexpectedly.
  
• Fixed an issue that caused the Settings page to close unexpectedly.
  
• Fixed an issue that caused profile folders to get very long (which might lead to max_path issues).
  
• Fixed an issue with unexpected notifications displayed to the user.
  
• Fixed a PowerShell console issue that created random line breaks.
  
• Fixed an issue that prevented a delegated user with required privileges from importing Group Policy Objects
  
• Fixed a Windows Management Instrumentation queries issue that could affect Patch Management.
  
• Fixed an unnamed issue with object performance counters.
  
• Fixed an OneDrive files on demand error on systems with User Experience Virtualization enabled. Fix requires setting the Dword HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\UEV\Agent\Configuration\ApplyExplorerCompatFix to 1.
  
• Fixed an issue that caused applications to take a long time to open.
  
• Fixed an AppLocker issue that prevented apps from running even if they were allowed to run.
  
• Fixed an AppLocker issue that sometimes prevented applications from loading software modules.
  
• Fixed a memory leak in the CryptCATAdminCalcHashFromFileHandle() function.
  
• Fixed an issue that could prevent the cluster service from starting.
  
• Addressed an issue that caused the Minimum Password Length Group Policy to have no effect.
  
• Fixed an unnamed issue that caused systems to stop working and generate 7E stop codes.
  
• Fixed a sign-in issue caused by typing a space before the username on first sign-in.
  
• Fixed classification failures caused by the wrong User Principal Name.
  
• Fixed a stop error on Hyper-V host.
  
• Fixed an issue that displayed the Processor Frequency as 0.
  
• Fixed a sleep system call issue on Glibc-2.31 or later on Windows Subsystem for Linux distributions.
  
• Fixed shutdown delay issues caused by Microsoft Keyboard Filter Service.
  
• Fixed a transient network disconnection issue caused by enabling packet capturing.
  
• Fixed an issue that prevented connections from being responsive to TCP resets.
  
• Fixed an issue that prevented the logging of events 4732 and 4733 for Domain-Local group membership changes.
  
• Fixed a Security Assertion Markup Language scoping support issue in AD FS.
  
• Fixed an issue that logged incorrect IP addresses in audit logs for Windows Transport requests.
  
• Fixed an issue that caused Account activity cmdlets from executing.
  
• Fixed a logging issue with Server Message Block.
  
• Fixed an issue with the CsvFs driver.
  
• Fixed an issue with the Remote Desktop Session Host that failed to open the Start Menu for mandatory user profiles.
  
• Fixed an issue that could cause stop error 0xC00002E3 at startup.
  
• Fixed a Visual Basic 6.0 runtime error.
  
• Added new but unnamed functionality to the robocopy command
  
• Support for Direct Server Return configuration for container load balancers introduced.
  
• Time zone information update for Yukon, Canada
  
• Ability to sync Microsoft Edge IE Mode unidirectional session cookies.
  

Known Issues 

1. The long standing Asian language packs issue that may throw the error "0x800f0982 - PSFX_E_MATCHING_COMPONENT_NOT_FOUND".
   • Microsoft still suggests to either uninstall and reinstall the language packs, or to reset the PC.
     
2. Microsoft Edge legacy error "0x80704006. Hmmmm…can’t reach this page" when loading sites that use non-standard ports.
   • Microsoft suggests to upgrade to the new Chromium-based Edge browser, to use IE11, or update Windows 10 to a newer version.
     

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