Day before yesterday I experienced a random glitch where the textures of all the blocks turned into the pink and black blocks. This lasted for a few seconds then reverted back to it's normal state. I only mention this because it is the only thing out of the ordinary that I experienced before the mob glitch. The game continued to play fine after that. When I logged on the next day (today), all of the villagers I had been breeding had disappeared. I had some harvesting crops for me, the rest were contained in mine carts. My sheep, cows and horses that were either in fences or on leashes also disappeared. There were no leashes or minecarts left behind from the despawn either. Just the fence post was left behind. Strangely the iron golem farm still worked without any of the villagers present. I guess they were still connected to their beds and work stations?