Chunk reloaded in the middle of my house, looks different. 1.12!

So lately I've been working on a house. I spent a lot of time on this, and I was really pissed when I opened the world found out that oops! a chunk reloaded, taking out a part of my house AND the chunk looks completely different. I've been playing on 1.12 because the world is customized and 1.13 doesn't support that. I know this particular instance is irreversible, but what can I do in the future so that this doesn't happen.

also this is 1.12, but there is no option for that.