Server Crash on spawning Ender Dragon with crystals

So this has happened at least 3 times so far on my server, twice today. When someone spawns in the Ender Dragon, the server freezes up and crashes. I tried to recreate it myself without plugins, but couldn’t. When I put the plugins back however and tried to recreate it, it still didn’t happen. So I’m at a loss as to what exactly is causing it…

Here is the log of the most recent crash:

Currently on paper-325. Based on the log, it doesn’t look like a plugin is the one causing the crash, but I could be wrong. I hope someone here can help me figure out what’s causing this :confused: