Microsoft has released quality improvements to the Windows 10 servicing stack, the OS component that enables customers to receive and install Windows updates. The latest servicing stack update (SSU) also comes with a change in the way future SSUs will be deployed to Windows 10 devices. Microsoft also released the September 2020 Patch Tuesday security updates, with updates for 129 vulnerabilities, 23 of them being rated as critical severity. Microsoft strongly encourages Windows 10 customers to update their servicing stack to the latest available version before installing the latest KB4571756 and KB4574727 September 2020 cumulative updates.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-starts-bundling-servicing-stack-updates-with-cumulative-updates/