Microsoft has addressed a known issue causing the new Microsoft Edge web browser not to install from custom Windows 10 installation media including updates released on Thursday, March 25.

Microsoft Edge Legacy is also being removed if using Windows 10 install media bundling the KB5000850 non-security release preview update for Windows 10 1909 and Windows Server 1909.

“Devices with Windows installations created from custom offline media or custom ISO image might have Microsoft Edge Legacy removed by this update, but not automatically replaced by the new Microsoft Edge,” Microsoft explains.

Missing SSU behind Microsoft Edge deployment issue

Users will face this issue known issue only when their custom offline media or custom ISO images are created by slipstreaming the KB5000850 update without first adding the standalone Servicing Stack Update (SSU) released on March 25.

To avoid encountering this issue, you have to make sure to first slipstream the latest standalone Servicing Stack Update (SSU) into your custom install media before slipstreaming the latest Windows 10 cumulative update (LCU).

Windows 10 devices configured to receive updates through Windows Update or Windows Update for Business are not affected by this issue.

“Any device connecting to Windows Update should always receive the latest versions of the Servicing Stack Update (SSU) and latest cumulative update (LCU) without any extra steps,” Microsoft said.

Customers affected by this issue can manually install the new Microsoft Edge browser on their systems after downloading it from here.

Edge Legacy going away for good

The new Chromium-based Edge is the default Windows 10 web browser after replacing Edge Legacy, starting with Windows 10 Insider Preview Build 21313.

Microsoft officially released the new Edge browser in January 2020 with an installer designed to automatically replaces the browser’s legacy version.

Edge Legacy will be permanently replaced in all Windows 10 builds by the new Microsoft Edge on all systems after installing April’s Windows 10 Patch Tuesday security update.

Microsoft Edge Legacy is now displaying notifications alerting users to switch to the Chromium-based Microsoft Edge after officially reaching its end of life on February 12, 2021.

In November 2019, Microsoft also fixed an issue triggered by managed Windows 10 systems being updated from outdated installation media and causing Windows 10 certificates to disappear.