there is bug with 6th quest of mansion lust event. i got many common cards to do this quest but it didn't confirm

I don't have that event, so I don't know for sure.

But in events I've seen, there is sometimes a difference between having something (cards, fuses, research combos, arena chests, etc.) and getting something.  That is, you may have many common cards, but the quest is looking for you to get more common cards.  You'll have to earn them while the quest is open.

what is the q asking? , if is   : Obtain 1 COMMON character cards , be sure its a character card not item