Link to my world:
https://drive.google.com/file/d/1RiOfj5tAg1v-RegpzW73o8Hpz-PkLRZI/view?usp=sharing

As can be seen in the image above, a second Ender Dragon together with its own portal on top of the old one ended up spawning in my world.

I have already killed the Ender Dragon before in this world, and even harvested its egg which is currently in my Ender chest.

If you check the world I attached, you will see that it is a pure survival world which never had cheats enabled before, so it's not possible for me to have done it by myself.

Personally, I don't mind this occourence of weird world regeneration (not going to lie, I do fancy a second dragon egg), but I still thought that I should report it.

Although I already posted this world, I'll also tell the seed it uses, just in case:

-238153602