You upgraded the Symantec Endpoint Protection (SEP) clients to 14.2 Release Update 1 or later.
Since the upgrade the content for Host Exploit Mitigation is not updating.
This occurs in environments where the Symantec Endpoint Protection Manager (SEPM) is on lower version than the clients.
In 14.2 RU1 a new moniker was added for CIDS 14.2 RU1.
{55DE35DC-862A-44c9-8A2B-3EF451665D0A}: SEPC CIDS Signatures 14.0 - MicroDefsB.CurDefs - SymAllLanguages
{0D03AEA1-B630-43F8-828E-F10E80A68B99}: SEPC CIDS Signatures 14.2 - MicroDefsB.CurDefs - SymAllLanguages
{02335EF8-ADE1-4DD8-9F0F-2A9662352E65}: SEPC CIDS Signatures 14.2 RU1 - MicroDefsB.CurDefs - SymAllLanguages
An SEPM on older version will not have above moniker
Upgrade the SEPM to 14.2 RU1 or later or allow the clients to update from Symantec LiveUpdate servers or LiveUpdate Administrator.