Windows 10 build 17120 (rs4 release)

Windows 10 build 17120 (rs4_release) is the twenty-first Insider Preview build of Windows 10 April 2018 Update. This build was released to Windows Insiders in the Fast Ring on 13 March 2018, then to Slow Ring users on 16 March 2018.

Changes

 * Performance improvements to Windows Defender Application Guard (WDAG).
 * You can now download files from within WDAG to the host. This feature is only available in the Enterprise SKU and must be turned on via Group Policy. To enable it, open Local Group Policy Editor, navigate to Administrative Templates, then navigate to Windows Components, and then go to the Windows Defender Application Guard item. Once here, select "Allow files to download and save to the host operating system from Windows Defender Application Guard", and on the dialog that comes up, toggle the option to "Enabled" and then click apply.
 * General improvements, changes and bug fixes listed in the official announcement.

Mixed Reality

 * If you're using a hybrid laptop, performance of Mixed Reality may be significantly reduced.
 * Sometimes inbox apps will fail to load inside Mixed Reality and newly placed holograms may be empty. Restarting should fix both issues.
 * Windows Mixed Reality will crash if you open the Microsoft Store from Movies & TV and then close both apps.
 * The ambient sound in Skyloft is louder than it should be.
 * On laptops with hybrid GPUs, the video does not render for 360-degree videos rendered directly in the Edge app. Sound can still be heard though.
 * The 360 viewer fails to launch from the Store app when you click on the "Launch" button after installing the 360 Viewer Edge extension. To workaround this bug, manually launch Edge and then enable the 360 Viewer extension.

Other

 * If you have the Dolby Access app installed along with an expired Dolby Atmos system, the Windows Audio service can crash with a stack overflow exception and as a result, the PC will not have sound. Uninstall the Dolby Access app to restore sound.