With DLP 12.5 (or newer), Reinstalling an Endpoint server that has existing Endpoint Agents results in Authentication errors within Agents Overview
Authentication Failure: Incorrect Tool Key is used during communication
Endpoint .jks files were not backed up during reinstallation of the Endpoint server
Copy the endpoint .jks file off of another Endpoint server. .jks files are located in \SymantecDLP\Protect\Keystore directory.
Restart the Vontu Monitor service once you copy the missing keystore files to the reinstalled Endpoint server.