Symantec Data Loss Prevention (DLP) is failing the establish a handshake with the SharePoint 2016 server.
The Wire Shark trace does not show any indication of a TLS handshake.
This started sometime after upgrading DLP from 14.6 MP3 to 15.1.
Initially, after the upgrade, the handshake was occurring as expected.
Unknown change on the network.
The solution was to ensure the domain name preceded the DLP Service Account name in the System-Settings-Credentials (separated by a \)..