After upgrading to, or installing Symantec Endpoint Protection (SEP) 14.3 RU2 or 14.3 RU3, an error message is present in the SEP client UI which reads
Proactive Threat Protection is not functioning correctly. Your protection definitions may be damaged or your product may be corrupt.
Once a SEP agent is in this state it may also fail to download and apply new definitions.
For several minutes after system startup the SEP client UI may not open and an error message that some SEP services are stopped will pop up.
This issue is fixed in Symantec Endpoint Protection 14.3 RU4 (14.3.7388.4000). For information on how to obtain the latest build of Symantec Endpoint Protection, see Download the latest version of Symantec software.
Stopping and starting SMC can temporarily resolve the issue until the device is restarted.
ESCRT-7787