My friends and I started a realm a few months back. We had a good 150 villagers between two player villages and 3~ world villages. One day, all of the villagers disappeared without a trace. Doors left open, workstations unattended, cats looking for owners. So we though "oh well, just cure one" as even the natural villages' villagers were gone. After 4 cure attempts, the villagers vanished the second they were cured. Went like this. Zombie villager > being cured > gone. It's like villagers hate banned from existing.  Villagers simply refuse to exist, and we don't particularly want to restart our realm just yet. this started in 1.16.5, but even carried over and continues now