There is a bug that has been identified with Unreal Engine version 4.12 that can impact PlayUp users. If you have nested entities, and one of the parents of the nested entities is mirrored, UE4 is currently not properly keeping the world transform information for the entity when it attaches it to the parent entity in the world outliner.
You can read more about this bug (UE-33380) here:
https://answers.unrealengine.com/questions/436476/bug-412-attachtocomponent-keepworldtransform-causi.html#comment-436476-form
