I cured multiple zombie villagers in my world only to find some random amount of time later that they vanish, this however is not the same with all of the villagers in my base, some have been around far longer than others. I know they were not killed as they were fenced off and it is impossible for mobs to spawn in their enclosure as the light level is too high. I really hope a fox for this comes soon as i spent a very long time building enclosure and curing villagers and i would like to know that it wasn't all a massive waste of my time