Microsoft Defender users will see new issues with recent updates, at least for Windows 10 20H2 updates.
According to reports from several users, the latest updates to Microsoft Defender for Windows 10 appear to be causing issues for users of older versions of Windows 10.
One of the issues reported and mentioned by the Borncity portal is the high memory usage of Microsoft Defender-related processes in addition to the slowdown system, along with login account errors when opening some applications (such as Office 2016) while the service is running.
The issue appears to be related to a service level error and appears to have a greater impact on Microsoft Defender for Endpoint users – but it also affects users with basic versions of Microsoft Security.
The bugs began reporting more than a month ago, but so far Microsoft has not confirmed any specific issues.