sometimes if the blocks are that fast, that you don't have hashed on that block.
that means that your workers are busy with others blocks.
if you have luck that you mine a block and find him really fast you get more pay out (if i am not wrong)
I don't think so. I also couldn't get any payment with 5 found blocks which took some time not found in a seconds.
My last payment came from 30,681 after that one, I couldn't get any payment so far (now we found 6 more blocks after that with no payment..)
My miners up and working without problem. It looks like there is another problem appeared with pool..