I suspect it is the drought, I live just west of Tweed Heads and planted a leopard tree last winter and it was the same as you describe until we got good rains from early December until now (we are not in drought here). Also mine, along with my crepe myrtle and hammer-leaf frangipanny (Plumeria podica), a tree of the tropics, also produced no new growth until this time. I also put it down to the cooler weather this year, or the late onset of the normal warmer conditions - I've heard reports this has been the coolest summer on record in this area at least until now. The others you see about that are healthier might have better underground access to moisture, eg. septic tank drainage, natural downhill underground runoff, etc. Not much help I'm afraid, good luck I hope it rains for you.