From what I can see in the picture the leaves are dropping off the smaller of the two canes? If so, the smaller one is probably the older of the two. As the plant ages and kicks out new growth often the older canes will drop their leaves around the same time. Leave the old cane there as the plant will continue to draw energy from it.
New growth is always a good thing and usually means the plant is happy. Good job!
BTW, your plant appears to be a phal type so is evergreen, needs intermediate temps and no winter rest.