Chuck area are being resetted/regenerated on 0.15.1

I was on a realm with other players and the host build a stable and half of it was gone and was replace with grass and trees. While after we fix it i noticed the host's was gone and half the Bridge to it. Thats I notice the chucks regenerated. The cave under he's house was gone or changed too. I notice this happen on my single player world. There was a big cave opening by my house and one day half of the cave closed up and a new tunnel was made.