I had a situation when windows clients are not reporting in WSUS server. To fix it I’ve used this small script at the clients.

@Echo Off
Echo Deleting Registry Keys - SUS Client ID
REG Delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v SusClientId  /f
REG Delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v SusClientIdValidation  /f
Echo Stopping Services  
net stop wuauserv /y
net stop BITS /y
Echo Removing Unwanted Files
rd C:\WINDOWS\SoftwareDistribution /s /Q
del "c:\windows\windowsupdate.log"
Echo Registering .dll in the Library
regsvr32 WUAPI.DLL /s
regsvr32 WUAUENG.DLL /s
regsvr32 WUAUENG1.DLL /s
regsvr32 ATL.DLL /s
regsvr32 WUCLTUI.DLL /s
regsvr32 WUPS.DLL /s
regsvr32 WUPS2.DLL /s
regsvr32 WUWEB.DLL /s
regsvr32 msxml3.dll /s
Echo Starting Services
net start wuauserv /y
net start BITS /y
Echo Updating Group Policy
gpupdate
Echo Reconnecting With WSUS Server
wuauclt.exe /resetauthorization /detectnow /reportnow
Echo Wait 10 Minutes for Client to Check In
Pause
exit