Setting the parent of a transform which resides in a Prefab Asset is disabled to prevent data corruption (GameObject: 'RoomContainer'). code example

Example: setting the parent of a transform which resides in a prefab

//You might have tried to set the transform of the prefab as the child
//instead of the transform of the object you instantiated by accident.
GameObject name = (GameObject)Instantiate(namePrefab);
namePrefab.transform.parent = nameOfParent.transform; //Wrong
name.transform.parent = name.transform; //Correct