Ok, I think I've got it. The visualizer seem to display the state at the very beginning of the turn when stepping frame by frame. The complete turn is
This means that between this visualization and the next, there are going to be both moving and
attacking. So the only way to actually display the attack, is to do it before combat.
I've looked a lot at games by stepping frame by frame, and this has been nagging me. But I notice now that when hitting "play" I can actually see how ants get into the combat position that ends up killing them.
Thanks for prodding me in the right direction!