CPU Metrics are not displayed in the APM Agent.
APM Agents - all releases.
The platform-specific statistic jar file may not be available in the AGENT_HOME/ core/ext directory.
Ensure that the introscope<platform>Stats.jar file relevant for the platform that the agent is running exists in the AGENT_HOME/ core/ext.
e.g. for Linux 64bit - ensure that introscopeLinuxIntelAmd64Stats.jar exists in the above directory.
If it does not exist, copy it from another agent of the same type/version or from the agent installation media.