I assume it would need to be something with a PreBattle test and NumFriendsInBattle - you should be able to rule out trait and anc. triggers quite easily, just by making back up of the files and deleting entire trigger sections, if you've got script obviously try running without it and see if result changes.
Question does it CTD when you've got beyond scroll, ie onto loading bar? If so I wonder if that faction could be missing something for the ally battle banners (though I thought that would give you white banner not crash).
Also are generals involved?
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