https://www.bleepingcomputer.com/news/microsoft/windows-update-kb4497936-for-insiders-brakes-windows-sandbox/

Microsoft says that the Windows Sandbox may fail to launch on systems where users have installed the KB4497936 Cumulative Update for the Slow, Fast and Release Preview rings of the Window Insider program.

As described by Microsoft on the known issues and notifications page for the latest Windows 10 version, "Windows Sandbox may fail to start with 'ERROR_FILE_NOT_FOUND (0x80070002)' on devices in which the operating system language is changed during the update process when installing Windows 10, version 1903."