I recently had an issue with an OEM agent 18.104.22.168 version running on Solaris. Looks like there’s a Java related bug which causes the agent to consume high amounts of CPU in the box. But the interesting part is this only happens when Listeners are being monitored. If you blackout the Listener targets this stops.
If this’s the case then you are hitting Bug 15953286.
The solution is comprised by various steps outlined on MOS “EM 12c: Enterprise Manager 12c Cloud Control Agent CPU Spiking and High Utilization on Solaris with Many Database and Listener Targets (Doc ID 1536871.1)”.