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

A question arose regarding an AI bug: when a weak enemy stack (let's call it "unit one") approaches my phoenix/dragon with the intention of forcing it to attack and damage a friendly stack with its retaliatory attack, it positions itself on the correct hex but doesn't attack!
Is this a bug in the AI or in the game engine? And what is the nature of this bug?
If needed, I can provide a save file with a description of the turn order in the battle that leads to this situation.