After the registration of a new Detection Server, no policies are actually loaded on the Detection Server.
Enforce shows event 1202 "No policies loaded" or 1201 "Loaded 0 policies".
Any supported version of DLP
In this case a Network Monitor did not have NPCAP installed correctly, which meant that the Detection Server had not fully started up - therefore no policies were accepted.
Policies are only sent from Enforce to a Detection Server when the latter is newly registered, or if a service restart or other policy changes occur.
The workaround is to restart the DetectionServerController service (aka the MonitorController service) on Enforce to reload all policies.
For more details about PacketCapture process and other possible causes, please see this article: Packet Capture service will not start due to NPF driver not properly installed on Network Monitor.