When entering the End, terrain generates very high, up to almost y=200. (Previously I've never seen it generate above "sea level.") The pillars are buried underground, and the dragon spawns underground and eventually flies to the top. The portal is on the very top. When respawning the dragon, the pillars stay at the generated spot.

The seed that I'm using to test this is -65638925627489590

Videos of the bug are https://youtu.be/sB1nVhQmxA4 and https://youtu.be/JJwKa1MAk0M (couldn't upload because of file size limits)