Underground mineshafts that are exposed by features (such as ravines) to the surface get erased

I loaded up a world so I could try out a new datapack I was making as a prank to craft bedrock to troll a friend. Pretty close to spawn, there is a ravine. A mineshaft cuts through it, but on one side there is just a random floating wood block because the rest of it got erased. There was no lava near it at all. The seed is -265197757783082813, and the coordinates are -240 40 240. It is very close to spawn, just a little ways south, so you might not have to even teleport.