When upgrading DLP 16.1 Beta to 16.1 GA release, you upgraded the detection servers but they fail to connect to Enforce.
Upgrading from 16.1 Beta to 16.1 GA
This is expected behavior due to a Beta release. You must first upgrade all detection servers to 16.1 GA and immediately upgrade Enforce to 16.1 GA release. Once this is complete, all servers should connect perfectly fine.