When a client or downstream server contacts WSUS, it uses the SusClientId and SusClientIdValidation registry keys located in HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate to identify itself. If you've cloned your downstream servers, a normal SysPrep will not reset these values. If more than one client or downstream server has the same SusClientId, they will just overwrite each other each time they update with WSUS.
Deleting these two keys on your downstream servers then rebooting should fix the problem.
I just solved this same problem on my cloned downstream servers. The GUID for replica downstream servers is held in the database.
Install SSMS locally on the downstream server and connect to the WSUS database.
Run this SQL:
update [SUSDB].[dbo].[tbConfigurationA] set serverid=newid()
Start the sync on the downstream server again - pretty much immediately, you'll see it populate on the upstream.
Note: If you do this on all downstream servers, you'll be left with a legacy duplicate server as nothing will own the original GUID. You should be able to just delete this - identify which one it is by the sync datetime.
When a client or downstream server contacts WSUS, it uses the SusClientId and SusClientIdValidation registry keys located in
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdateto identify itself. If you've cloned your downstream servers, a normal SysPrep will not reset these values. If more than one client or downstream server has the same SusClientId, they will just overwrite each other each time they update with WSUS.Deleting these two keys on your downstream servers then rebooting should fix the problem.
HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\SusClientIdHKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\SusClientIdValidationI just solved this same problem on my cloned downstream servers. The GUID for replica downstream servers is held in the database.
Install SSMS locally on the downstream server and connect to the WSUS database.
Run this SQL:
Start the sync on the downstream server again - pretty much immediately, you'll see it populate on the upstream.
Note: If you do this on all downstream servers, you'll be left with a legacy duplicate server as nothing will own the original GUID. You should be able to just delete this - identify which one it is by the sync datetime.