Have you already tried to add Debug.Logs to your code to see what is going on during runtime? Maybe something is calling the AttackerSpawned method which is not supposed to call that method.
Good job. According to the window at the bottom, AttackerSpawned gets called in the Attacker class only. This means that the problem is somewhere “near” the Attacker object/component.
Maybe there are superfluous Attacker components in your scene. Have you already checked all your game objects in the Hierarchy.