Chunks duplicating nearby

I loaded 17w14a, and I found near my base (which is a mountain)
in water 70 blocks away the same duplicated chunk over there.. a mountain end rods and so on. chests that were in the chunk were duplicated, but the chests didn't contain anything. Now when I loaded 17w15a the chunk in which my beacon was in, some iron blocks and the ladder to get to the beacon (my mine) was duplicated. Although this could be a good thing, I don't like cheats and above ground it's ruining my landscape. biomes that the chunks were in are also doing this.
I first encountered the issue back in 1.8.2 or so when my previous world had swamp biome chunks in my extreme hills. Please help this has been an issue for a while, even when loading a realised update not snapshot.

Please respond!
Minecraft Username: Demn8