Often the reason for a plant not coming into leave in the spring as early as it would normally or at the same time as plants of the same species is that it has suffered some sort of shock. For example if it was potted up or re-planted as a bare root plant during the winter or it has had some major local climate change such as being growing in a green house and then moved out side.
The only course of action is to wait and see if the plant breaks but and leafs up later. Its not unheard of for such plants to break bud in June