Microsoft has released a new Windows Defender update that fixes an issues with SFC /scannow detecting corrupted Windows Defender PowerShell files. The issue has been resolved as of version 4.8.1908. Users will also need to run the following DISM commands in order for the issue to be fully resolved. After this update is applied, PowerShell files that are part of the Windows image are not changed, and the SFC tool no longer flags these files, Microsoft has stated that they have released the update.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-fixes-corrupted-windows-defender-files-when-using-sfc/