Unity C# instantiation bugged compared to editor instantiation

Question

I have a zombie prefab that, if I drag it into a unity scene will find the player run up to him, stop, and start attacking doing one damage to the player who has 5 health. If I instantiate it from the prefab in C# the zombie runs right through the player and instantly kills them dealing 5 damage instantaneously. Is this just an instantiation bug? If I clone a zombie currently in the scene with the instantiate method it will behave properly... What am I missing in this process?