Turn 5, South Pole vs. Siple 4v2 attack fails. 3 leftovers.
What are the odds of that happening?
That cannot happen. I suggest checking history and looking more closely -- ensure the territory you're attacking really had 2 when your attack occurred, that you really attacked with 4, that the game is really set to 0% luck, and that the offensive/defensive kill rates are standard. One of those things will be untrue.