For clarification this was on running on a 1.15.2 bukkit server, with McMMO, however I doubt this would have effected my issue.
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.
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run modified server software.
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