All of the mobs I had near my base in farms de spawned

When I got on to my survival world today I realized that my horse, sheep, and cows had de spawned. After looking I found my dogs, villagers and armor stands had also despawned. The only thing that hasn't despawned are the villagers in my iron farm (but the farm did brake as the golems are now spawning on top of the beds instead of in the water). Also the red stone clock in my creeper farm turned off. Sorry if I seem upset but I don't want other people to lose so much of their hard work.