Corals are funny things to keep and can succeed or fail, sometimes for reasons that are not clear. Xenia is typical of this trait. For some it grows like a weed and is a problem, for others it just will not grow for them.
A lot of people here have that one coral that is supposed to be very easy to grow, but they just can't seem to get it to live for them.
A small move can make a big difference in lighting, water flow, food supply and so on.