To start the combo with....

Brutal Swing you need to attack from the side of the target. So maybe first time you did not hit him from the side exactly.

Patch of Storm combo is started from behind the target.

If you are quick enough you can run through the mob to the side or rear and use the action when at location, more then likely you will be fast enough and use the action before the mob changes directions. Even though the mob moves during or right before the action animation.