i had a iron golem farm with 10 villagers all contained in a 7x7x4 room made of glass blocks  and fletching tables integrated into the walls the whole area was well lit with torches  , this glass room was positioned directly ontop of 21 beds in a 3x7 arrangement this room and beds was 3 blocks above the golem spawn platform . i switched the game on one morning and noticed golems were no longer spawning so i went up to investigate and sure enough all the villagers had turned to zombie villagers with no way for any zombie to enter or spawn in the room my only thought could be that maybe they all turned from being unable to sleep but have found no information online as to say that villager turrn if they dont sleep