Please kindly make sure that the v-cut lines, cut outs, millings and slots are in the same layer with the board outline. If it is not in the same layer with the board outline, it will be missed. So please kindly check it before you place your order.If it is missed due to they are not in the same layer with the board outline, we will not responsible for it.(If the slots are to be plated, it needs to be with the drill holes in the same layer, or it will be missed easily).
From https://support.jlcpcb.com/article/68-instructions-for-ordering: