If an alliance loses many enough members during a war season to fall below the minimum amount of members that is required for an alliance to be allowed to further participate in the wars, then this alliance will automatically be removed from the map, i.e. losing its fiefdoms. Those fiefdoms will then be redistributed to other alliances on the map.
So far, that is an intended behaviour / game mechanic and no bug.
Then, regarding which alliance(s) will receive those redistributed fiefdoms, I have no idea how that is decided. Maybe this is just random and killer / vicjos were just lucky.
I know, it’s always unsatisfying when opponents get favoured by luck in a competition, but I wish you best of luck for the remaining season time!