Minecraft Nether chunks in the Overworld - Chunk error/corruption - What I did to fix it.
Here is a super rare corruption or chunk error that I came across in my world. Nether chunks appeared in the overworld, almost like when new chunks and old chunks would leave a sharp edge. I was able to fix it because it turns out it was a whole region and I was able to copy an old region file over the corrupted one. Not sure what caused this but I've never seen it documented anywhere.