When you try to drag and drop a variable name into the Message text box in a DLP Response Rule in the Enforce Console it inserts text similar to the following which is not correct variable syntax:
javascript:addSubstitutionVariable(0, '$INCIDENT_ID$', 'notifySubject')
All in-service DLP versions.
You cannot drag and drop the variable into the Message text box as this will insert invalid text causing the response rule to not work.
Simply click on the variable name in the "Insert Variable" list you wish to insert into the Message text box and the correct variable syntax will be used.