bot.Inventory.Contains is not able to retrieve items from the inventory, if you log the result from the contains with any item and quantity that is present in your inventory it is returning false. I'm guessing that the method is also used with KillForItem because that too doesn't stop killing the monster when the bot picks up the item.
You should be able to reproduce with any item and quantity with bot.Log and toString() the boolean returned. This is working fine last week. Confirmed item names with grabber so it shouldn't be incorrect string within the method call.