The ender dragon keeps spawning in every time I go more than 800 blocks from spawn. Is it something with the seed?

I’ve been playing on this world for 2 years and in August of 2024 me and my cousin spawned in the ender dragon. We spawned it in twice, one right on spawn, and one maybe a thousand blocks away. We killed it both times and nothing happened with it until today when I flew 1500 blocks from spawn and when I came back the ender dragon was spawned. I didn’t know why this happened but I had multiple copies of this world and found out that if I went about 800 blocks from spawn, then the ender dragon will spawn in. I have been pretty much only been using this world for the past 2 years and have so much built on it, and if I can’t figure out to stop it from spawning I will probably have to start a new world. Does anyone know why this is happening and how I can stop it from spawning in?