THIS WAS PREVIOUSLY RELEASED UNDER A NON VANILLA VERSION, I TESTED IT ON VANILLA AND THE ISSUE STILL STANDS.

I was fighting the ender dragon as I normally do, running around on the pillars breaking the crystals and placing water buckets on the top so they flow down. However half way through I noticed that the ender dragon got stuck flying underground in a roughly 30 block radius under the water, you could only see his wings and somethings the rest of his body above the endstone. He continued to fly in a figure 8 pattern between two pillars that were submerged in water so the ender dragon was under water the entire time. After destroying all the crystals I attempted to free the ender dragon by removing the water buckets. After removing the water the dragon immediately broke out of the loop. This kind of ruins the entire boss fight as you only need to pepper him with a few arrows with zero threat of counter attack.