The SIEM report shows that some devices, such as VM003 (Critical server) and NET003 (IPS), are DOWN and therefore not reporting logs. In security monitoring, the absence of log data from critical systems creates dangerous blind spots. If logs are missing, attacks can proceed undetected, or investigations may lack the data needed for incident response.

The most effective action is to perform a non-reporting device assessment (C). This means identifying and correcting issues where devices fail to send logs, whether due to outages, misconfigurations, or integration gaps. Ensuring all critical devices, especially servers and intrusion prevention systems, consistently send logs to the SIEM strengthens overall visibility and monitoring posture.

Option A (time calibration) is important for correlation accuracy but does not address missing log feeds. Option B (centralized use case library) enhances detection but only works if the SIEM is receiving complete data. Option D (resiliency plan) helps protect log retention but is irrelevant if logs are never received in the first place.

Therefore, fixing non-reporting log sources is the highest priority to improve monitoring effectiveness.