I can confirm this is a newly-added bug introduced with the Nether Update. I was away from my main village when the update went live, and after going back to it several days later, half my Villagers were gone. They had been named with Nametags and were constrained by walls, so they couldn't have wandered off. Since the chunk was unloaded, there were no hostile mobs that could have spawned and killed them. One of them, a Librarian, was contained in a "cubicle" to keep him safe, so he didn't have the room to roam that usually leads to mobs despawning.
KG
I can confirm this is a newly-added bug introduced with the Nether Update. I was away from my main village when the update went live, and after going back to it several days later, half my Villagers were gone. They had been named with Nametags and were constrained by walls, so they couldn't have wandered off. Since the chunk was unloaded, there were no hostile mobs that could have spawned and killed them. One of them, a Librarian, was contained in a "cubicle" to keep him safe, so he didn't have the room to roam that usually leads to mobs despawning.