I was practicing to defeat the ender dragon when the ender dragon killed me as usual. When I went back to the end however, I could hear the dragon, but I couldn't see it or attack it. Even the /kill command wouldn't work. However, it could still attack me by both ramming into me and breathing fireballs.

Steps to reproduce:

1. Go to the end and go to survival.
2. Kill the player
3. Go back to the end. 

Edit: It happened again! Please fix this bug.