Tried to respawn the ender dragon using the ender crystals. It played the animation and spawned new towers and crystals on top of them. The dragon did not respawn. We tried again and the crystals blew up with no other effect. After trying this 2 times we deleted the DIM1 folder and reloaded the end a few times on different difficulties.
Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w42a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.