WSUS and Domain Controllers/Servers – Help Please!

Here is my scenario:

Workstations are working flawlessly. However domain servers lost the ability to manually check for update.

Newly installed WSUS server:
-Created OU and added all the workstations from each location to it.
-Created Security group inside OU for each location and added the workstations to it.
-Configured WSUS GP and linked the OU.
Linked the Security group under the Security filtering inside the GP.

What am I missing here?
Any server that is a domain member is located under the Server OU in its respective location.

Any help is greatly appreciated!