Recently I noticed some machines have disappeared from WSUS server. The machines that are not reported in WSUS are in the OU they are getting the Group Policy update and they know WSUS server. When I login to each workstation and type in CLI wuauclt.exe /detectnow and then the machines appears in the WSUS console, but then some other client machines disappears.
This is old known issue since Windows XP time.
This issue occurs if the computer was set up by using a sysprep image, in which the registry value for SusClientID is populated before it is deployed to client computers.
When you use Sysprep to generalize an image for a machine, or when you use a unique SID-generating technology to create the images, the SusClientId registry value is not cleared if it is populated within the image before the image is deployed.
To resolve this issue you need to delete “SusClientID” and “SusClientIDValidation” registry values from HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate
