The bug

Zombie villagers with Gossips (from being a normal villager previously) do not keep their Gossips data when the world is saved and reloaded (on singleplayer).

How to reproduce

1. Have a villager with some Gossips
2. Convert the villager into a zombie villager, the zombie villager keeps the Gossips from before
3. Save and quit the world
4. When the world is reloaded, the zombie villager no longer has the Gossips