Tonight CB registered my final damage on NM but I didn't get the appropriate chest because someone finished off boss before my run completed. I didn't post this in technical issues as I am sure this is working as intended, but it seems like a poor design flaw. Most other mobile games if you register damage on the raid boss then you get credit. That's why there is a tabulation period. Just saying it's a crappy way to lose a key, when there is a million other ways we lose our keys.