DATA IS LOST ON A WORLD.

I am sick and tired of this issue, this first happened on my hardcore world and now my survival multiplayer world with my friend, I have spent hours collecting items, mining. I leave the world for one moment and come back to stuff missing (I'm not sure if it's also due to me switching shaders off and on, but leaving the world is the main reason I think for this happening), the furnaces I just placed, the diamonds I collected or all the ores, obsidian, resources I collected within this time period disappeared, it went back to what I had before, still stuff in chest (What I had before, removed everything I had collected now). This bug has to be fixed, it causes me to have to restart from where I was before!

THIS ISSUE HAS TO BE FIXED.