This warning is observed in Symantec Endpoint Protection (SEP) clients when Web Extension (WebExt) content is unavailable. It has been observed disabling the feature through the Intrusion Prevention policy does not solve the problem in air-gapped environments.
Path to verify WebExt Content: C:\ProgramData\Symantec\Symantec Endpoint Protection\<Version>\Data\Definitions\WebExtDefs
WebExt content is unavailable.
This issue have been fixed in 14.3 RU9