I just had this same thing occur - Built a trading hall last night - fenced in 13 villagers in separate spaces and gave them a bed, 1 open block to stand, and the designated workbench. After I got them all linked to the right beds I observed them sleeping and working as they should. This morning I logged into to show someone my trading hall and all the villagers were asleep in their beds, logged out and back in about an hour later and all 13 villagers have vanished.
I will note that my trading hall is currently only 2 blocks tall so if what Specialistol said is true then I can see they likely stood on the beds and suffocated when the realm loaded up for me. so many zombie villagers converted all for nothing 😞
My skeleton spawner still drops bows but I'm not getting any enchanted bows and it looks like the bows are all full health, no damage.
My zombie spawner now drops nothing but rotten meat.