I have 22 downstream servers and i can see only 2 on the upstream.
and some time the downstream server shown is changed but still only 2
When a client or downstream server contacts WSUS, it uses the SusClientId and SusClientIdValidation registry keys located in
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:
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.