Some villagers have rendering problems with their overlays depending on what biome (Desert, snowy, or swamp), or profession. This wasn't an issue from previous 1.12 betas or the latest 1.11.4 version.

Desert Biome

The weaponsmith loses the "head" layer when spawned in a desert.
Librarians desert "head" layer is shown when spawned in the desert. (Seen underneath the librarian's red book on their heads.)
Cartographer "head" layer is missing.

Iceberg/Snow Tundra Biome

The weaponsmith loses the "hat" layer.
Cartographers also loses the "hat" layer.

Swamp Biome

Weaponsmiths will lose ther "lily pad" head layer when spawned in a swamp.
Cartographers loses their "lily pad" layer.

Savanna Biome

Weaponsmiths loses the "Laurel wreath-like" head layer.
Cartographers also loses the "Laurel wreath-like" layer.

Note: Cartographers and weaponsmiths from 4 biomes are missing their head layers, while the librarians have the desert head layer visible.