Error Message :
The Command :REGISTER_VARIABLE will fail if the Agent it is processed on is on a lower Automation Engine (AE) version than 11.2, it will work without problems on an agent 11.2 (or probably higher) but the command is ignored if the Agent is on a lower Version.
There is no error message displayed, but the command is not processed.
It is not described in the Documentation, as a pre-information it is described as known error.
Root Cause: The behavior itself is by design, older Agents do not have the function :REGISTER_VARIABLE to handle this command, but it is not described in documentation.
Update to a fix version listed below or a newer version if available.
Fix Status: Released
Automation Engine 12 - Available
Automation Engine 11.2.2 - Available