No dragon ball from about 70 mobs at papaya

So I am lvl 70, and I was hunting dbs at papaya, killing mobs of lvl 67-69. Killed like 70 or few more mobs, but not even a single db. In the previous hunt, I easily got 2-3 dbs by killing this much mobs.

I know it is based on luck. But 70 kills and 0 db, is it really bad luck or maybe something wrong? Something related to drop rate maybe?

Quote from Quvades

no all is ok
i found 4 db in 2 hours with lvl 50, a friend get all 7 in 2 hours with lvl 65 and one guy in the the chat say he get all 7 in 20 minutes after that he get nothing you are only have bad luck

Oh okay, I see. Hmm..