Worked here as well, thanks.
Anh, I'm having another problem (but it was there before your update). In the same code example, when you create the nested cloneable groups it is possible to sort and drag them anywhere, like for example move a child to same level as its parent or even move a child to a different parent. Once you move it, it'll break the Add clone button and I'm assuming it will mess up with the data in the JSON. Is there a way to avoid that?
Thanks.