So I was playing Minecraft and returning from a caving expedition and when I was returning to my home I saw am unloaded chunk. It appeared as giant hole in the ground all the way down to the void. Next mobs wouldn't respond or act in the world. There was a baby chicken simply staring at the sky and when broke the block under it, and placed water in the single block space and the baby chicken wasn't floating or reacting at all. Next my game began to lag like crazy. My settings are: Particles: minimal, Fancy Graphics, Normal RD, Advanced Open GL On, and Max FPS. I had been averaging anywhere between 16-22 frames with no lag. Finally I quit my world and tried to reload it, once it finally loaded (it took roughly 2 minutes) only a few chunks around me would load. I'm sorry about the lengthyness of this and I wish you luck in your endeavors!