HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

I wonder, is this bug related to the presence of a swamp, the presence of wyverns, or something else? Sometimes I've noticed in the game that enemies don't attack an open slot for some reason, but this happened only a few times, and I didn't pay much attention to it. I don't even remember in what situations this happened – I just attributed it to the AI's logic.