Just a quick note that Microsoft has recently release a hot fix KB4338819 that fixes and issue with the Mitigation option. This is a Windows Defender setting that can be found under the Administrative Templates>Computers>System>Mitigation Options setting.
The fix is described as:
Addresses an issue that may cause the Mitigation Options Group Policy client-side extension to fail during GPO processing. The error message is â€œWindows failed to apply the MitigationOptions settings. MitigationOptions settings might have its own log fileâ€ or â€œProcessGPOList: Extension MitigationOptions returned 0xea.â€ This issue occurs when Mitigation Options has been defined either manually or by Group Policy on a machine using Windows Defender Security Center or the PowerShell Set-ProcessMitigation cmdlet.