Update on party try.
Okay I have tried this with two people now as a party, when you fail the oath and the battle screen comes up, don't press close just continue to kill the boss. Once you kill the boss. Collect the cores dropped, but when I do that I don't get any items from the cores. I then hit replay on battle screen window and I can do the same battle over again. Those cores that were dropped didn't give me or my other char any item when I picked them up. Unless I did something wrong which I doubt it. This bug is useless and it doesn't work.