Is it possible to use mix version between clients and Automation Engine, such as client version 12.0.1 and Automation Engine 12.1.1?
You can use mix version between AE and agents and other components. However we strongly recommend you to upgrade your agents and components to match the major AE version for highest compatibility.
But the upgrade should be performed carefully step by step. You should backup your old agent & settings before installing new one, do testing carefully before switching to new agents and component version.