What I expected to happen was...:

I expected my world to load as normal, a lot of the terrain was built by myself. The rest was the natural world generation.

What actually happened was...:

What actually happened was many of the trees, structures were affected very oddly, dirt and vines and bamboo appeared randomly all over. Holes appeared in the ground with vines as well. I've attached screenshots displaying the changes as well as 1 (2018-11-10_17.51.47.png) which shows the same structure earlier in the week (It's the closest photo of the building to today's date as I have). 

Steps to Reproduce:

I've had this world since 1.6 so some world generation changes have caused chunk issues in the past but in the form of biome changes and terrain rather than affecting structures. I successfully reproduced the change on the world by restoring it to an old file and going back to 18w47a and the same thing happened. I am unsure if the same odd changes would occur on anyone else's world due to the age of my own.  (edit: I've read other people's reviews and while, unsure how to recreate it, it has affected other people)