You are seeing the "System Event Code 4206 - Managed PKI Service certificate has expired" on Symantec DLP Enforce (System > Servers and Detectors > Overview).
You have used the DLP Cloud Detection Service (CDS) in the past but are not using it anymore.
Release : 15.8
Component : Cloud Detection Service
This happens because, even though you are no longer using CDS, the certificates are still stored in the enforce_keystore.jks.
This has been filed as a defect, DLP-44120, to be fixed in a future release of DLP.
For those who are still using the Cloud Service, and seeing this or similar alerts, see related article: MPKI certificate errors in Servers and Detectors Overview for the Enforce Server (broadcom.com)