The "Reputation check timed out" event is annoying when an environment is isolated from the Internet. The External Logging->Log Filter configuration does allow for some control, but only operates on entire classes of events.
NOTE: The following configuration is specific to syslog-ng (https://syslog-ng.org/).
source syslog_udp { udp(port(514)); }; destination df_sep { file("/var/log/sep.log"); }; filter reputation_filter { not message("Reputation check timed out"); }; log { source(syslog_udp); filter(reputation_filter); destination(df_sep); };