This is a known defect in the product where the DC name is not being passed to the remediation action.
This results in the remediation action having no target and not running correctly.
A Defect request has been created to correct this in a future version of Active Administrator.
The defect ID is 515068.
Workaround:
1) Configure the remediation action separately for each monitored DC to include the "target computer' option.
This will trigger the remediation action to act on that DC specifically, rather than getting the DC to run on from the alert itself. This must be done for each monitored DC.
2) Run the remediation command manually when an alert come in.