If you have a low level of hashpower, I myself was doing a video comparison for a while with 10Gh/s hashpower and what would happen is that there is a minimum amount they would send each day, around 5430 satoshis, something around there and if your daily payout is less than that, then it gets kept by until it reaches that 5430 satoshi level, before going out.

It could be related to that. With my 10GHs account I would have one day of no payout then the next day I would get a payout as each payout was in the 4000 satoshi range so one day it would be 4000 then the next day, both combined would be 8000 so then that was more than the 5430 level.

On the payout page the payout that is saved will show up as zero but there is a info icon, a small i which if you move the mouse over does come up with information about the payout.

It also can be timezone related, the payouts are in UTC timezone I believe so if the payout is at 23:00 UTC then if you live in the far east then that payout would have been well into the next day so that can also give the impression that your payout might not be daily.

Ian