Hi,
I'm not sure if we have the same issue which we migrated to a new version of SEPM 12.1 to a new server too. I can deploy the client software but I can't view the client on the console.
With the help of Tech support, they suggest me to disable the communications between the management server and the clients under Clients > My Company > Security tab from my old server (SEPM 11.0).
After that, I can communicate to a new SEPM 12.1.
(Please see attached screenshot).