OnTriggerExit2D is not functioning with overlayed sprites.
To reproduce:
1) Load the project and open the CoreLoop.unity scene.
2) Run the scene in the player, and in the Game window, click and drag one of the green squares on top of (z-toward-camera) one of the knights. You should see them highlight as you drag the square over them.
3) Keep dragging the square beyond the bounds of the knight(s).

The result is that no OnTriggerExit2D call will be made, when I would expect it to be.