Zombie Villagers were updated to display their professions. However, they no longer have their biome overlays, they just apply their profession over the default zombie villager texture, which uses grey robes. The rank mark is also missing from their belts. See the attached picture.

This is caused by the fact that the game uses fully black pixels in the profession texture to determine which parts of the biome texture will be erased when displaying the model and fully white everywhere else, but all the zombie villager profession textures were ported directly with fully black backgrounds due to an oversight, which causes the entire biome texture to be covered.