For pin behavior, try using debug to confirm you are pinning to the correct object instance, picking instances can sometimes get tricky when referring to the same object.
Once you have pinned one to the other, you no longer use actions to move the pinned object. When you move the object it is pinned to, both will move.
In this situation though, you probably don't need the pin behavior at all. As both edges of your platform are the same object with different animation frames, an action that makes that object move should move both/all instances of that object at the same time. Just make sure the ones you want to move are picked correctly with conditions.