Anti-progress bug

So basically I am playing my single-player survival world and where I live in game gets reset to earlier times when I lived there with chests losing new items I put in and structures that I have just built disappear this happens if I go out of visual distance of the base, go into the nether or end and when I afk for several hours so if this s fixed I will be greatly appreciated. Also in one of the pics you see it but islands are appearing in the sea nearby.