The actions are executed during evaluation of the policy when the computer is added in violator folder. If the computer is already present in violator folder before the evaluation of the policy, the action is not executed again for the computer.
To force a new execution of the actions for a computer it is possible to remove it from Violators folder.
Right click on the computer in Violators folder and select Reset :

The computer is removed from the Violators folder.
The next time the policy is evaluated, the computer is added again in violators folder (if it is still returned by the associated query) and the actions are again executed for the computer.
Remark :
It is possible to configure an action to be executed when the asset no longer violates the policy.
In the properties of the action check the box "Perform action when Asset no longer violated Policy" :

With this option enabled, the action is executed only when the asset is removed from the violators folder during policy evaluation. (a manual reset does not execute the action).