Put the summary of the bug you're having here
*What I expected to happen was...:The Ender dragon to spawn Normally and be able to fight him just like I would do in 1.8.
*What actually happened was...:The Ender Dragon didn't spawn and the only way I could get him to spawn was go to another world
Steps to Reproduce:
1. It happened naturally and I don't know how to reproduce sorry.
2. ...
3. ...
This happened to me once, occurred after a strange chunk issue. He had not appeared before that point and did not appear after I rejoined the world.