I have this game in French.
the rules say:
Si un joueur possède 3 symboles Malchance sur un tirage de dés et/ou avec ses jetons, il doit immédiatement se défausser d'une de ses cartes CV actives.
This would translate as (emphasis mine):
If a player has 3 bad luck symbols on his dice and/or tokens he must immediately discard one of his active CV cards
So, if you get your 6 bad luck symbols during the same turn but not on the same roll, I would say that you discard a card when you roll your third bad luck symbol and then a second one (from the same column if you wish) when you roll your sixth one. Assuming you get the 6 bad luck symbols at the same time (now that's real bad luck) I would appply the same rule and allow discarding twice from the same column...