An issue was found where the Agent Unix would require huge amounts of memory within a short period of time after the upgrade from 21.0.4 to 21.0.4+HF.1.
Release : 21.0.4+HF.1
Software Bug
The issue has been confirmed to be a bug and was fixed with version 21.0.5 of the Unix Agent.
It is not necessary to upgrade the Automation Engine, only the agent needs to be upgraded.