When building an artificial village, place villagers in closed, well-lit houses so that mobs do not kill them, however some villagers have disappeared in the same way. This happened several times in different worlds, I already changed the location of the audeões and I took all measures to avoid escape and death, but still they disappeared with time. It is already tiring to replace villagers.
In the images I put the places where there were villagers, places with high walls and closed to avoid arrows, well lit to avoid zombies, without doors to prevent escapes.