Hello,
What version of SEPM are you running globally? From What version to which version was the migration taken place?
Are the GUP clients updated as well?
Are the Clients properly communicating to the SEPM Server and the GUP client machines?
Are the GUP client machines updated with the Latest definitions?
Troubleshooting Articles:
Troubleshooting the Group Update Provider (GUP) in Symantec Endpoint Protection (SEP)
http://www.symantec.com/docs/TECH104539
Symantec Endpoint Protection: LiveUpdate Troubleshooting Flowchart
http://www.symantec.com/docs/TECH95790
Troubleshooting Content Delivery to the Symantec Endpoint Protection client
http://www.symantec.com/docs/TECH106034
Could you upload us the sylink.log from 1 of the client machines which are not taking the updates. Check the Article on how to pull the sylink logs
http://www.symantec.com/docs/TECH104758
Hope that helps!!