There are three villagers in the picture as seen by the health bars. The border of the villager behind the palisade wall can’t be seen at all. The border of the villager behind the palisade gate can be partly seen as it’s on the edge of the palisade part of the gate.
I also discovered that the borders are not visible behind Lumber camps or Mining camps.
Although, the weirdest thing is that when previewing the placement of these buildings the borders of units can be seen, but when they are actually built they can no longer be seen. See pictures below.
usually when you place units behind buildings you can see a blue silouete (or whatever colour you are) to see the unit, this doesnt apply if units are behind palisades. Unless units behind a palisade are selected, there is no way to know they are there in the first place
This is worse in general. How many vills are there?
Three!
There seems to be an small transition between “visible as normal” and “behind the building: activate the border” where the unit is in fact not visible and has no border. If I move one villager a bit to the left and another a bit to the right, everything comes back to normal: