Villaggers dissapear while away in easyest difficult, survival mode

seed:805967637
survival mode
difficult: easyest (no zombies)

There is 3 village nearbly start point whit full of npc-s. I went down to the mine behind the first village, to explore it, i went down pretty far for hours. I surfaced and went back to village. All NPC was dissapeared from all the 3 villages. Since there is no zombies they cannot be eaten.