Put the summary of the bug you're having here

What I expected to happen was...:
I made the dragon respawn with the method of Ender Crystals and I expected it to be... normal? Like flying and attacking players. For endermen, well I didn't expected them to attack us if we don't look at them in the eyes.

What actually happened was...:
I made the dragon respawn, and he started to fly around a tower (the towers where the ender crystals are) and then, he started going down into the floor and staying there, so it's nearly impossible to hit it (and kill it). For the endermen, they sometimes target us without us doing anything.

Steps to Reproduce:
1. Kill the dragon.
2. Put water on each tower with ender crystal.
3. Put water all around the end main portal to the towers (I did it to repulse the endermen)
4. Respawn the enderdragon either with a command or with ender crystals to place on the main portal.
5. And watch!