I've seen villagers despawn in rooms with no doors - when there are only two left in a village you can throw food at them and throw food at them but they will not breed. The number of doors has not changed and in some cases it has increased but there are no new villagers. They may at some point display hearts but there will never be a baby villager. This same process worked in 1.10 but ceased to work in 1.11.
This has happened in several villages and several different worlds in survival in new worlds and old worlds.
In 1.11 they will no longer pick up food or harvest food.
This is not the same issue as listed as the duplicate - looking in the nbt explorer - the inventory slot for each villager is empty.