Black boxes appear either on random things. Sometimes it's just around the hitboxes (like arrows). When it happens to villagers they're completely black and in the shape of a farmer (no matter what profession they are). This happens randomly or at certain angles.

Ex: In the first picture, the text is in all black and the arrows' hitboxes are black.
In the other one, the villagers are experiencing the bug (Their professions are weaponsmith, leatherworker, and farmer)