So, I was just about to play minecraft and I saw that 1.12 was finally released so i decided to play it in survival. I went into a survival world with cheats enabled and the the world loaded, I saw what looked like a bunch of chunks randomly scattered where they're weren't supposed to be. I thought my computer just hadn't loaded the world yet but then I flew over to one of the chunk things and it let me go into an exposed cave.

Note: It isn't the seed that's broken it's just the world itself.