When a policy based on a keyword list is created, it does not trigger.

In Message Tracking > Policy Trace and in Policy Engine Log, the following error is observed:

mailgate PolicyEngine[4212]: TID 3935144816, ERROR: LexicalError exception from lxDFACompiler::CompileDFAFromLexStream(). Description: Error on rule 16, token '  '.; in
file: WssLexUtil.cpp; at line: 104

The error indicates that the keyword list cannot be compiled due to a problem with the Default Annotation Locale.
 
Most likely, the annotation's start and end contain a single break line tag (<br>).

Open MailGate Admin UI > Mail Policies > Annotations > Annotation Settings and edit each annotation start / end to contain something other than a single break line.