Ender Dragon disappeared

Tablet Android Samsung Galaxy Tab 4 8.0

Upon first entering the End, I died 2 times trying to kill the Ender Dragon when I returned to get my stuff and continue my assault on the dragon I noticed that it wasn't around and that the portal to the overworld was open. I hadn't killed the dragon actually didn't even hit it once. I was still in the process of getting the orbs. I have read reports on this happening in the past frequently so why haven't you fixed the issue yet.