Bitcoin transactions have 2 distinct states:
1) The transaction is sent out on the network
2) The transaction is confirmed in a block
The last 2 payouts are still in state 1)
They'll get to state 2) either when another pool confirms them (unlikely coz of the high transaction fees) or we find our next block

Can you talk a little bit about why this may be different from block-to-block? I totally get (or at least I think I do) that payouts for previous blocks may wait until a new block is mined by kano.is. What I am not clear on is why I would not get a payout (yet) when a block is mined by kano.is, when I did get a payout when previous blocks were mined (either for that block or for shares of previous ones).
IOW, I got a payout very soon after blocks 500622, 500907, and 501739. My understanding is that those payouts may have been for previously mined blocks. However, if that is the case, why would I not get a payout when 501835 was mined, for the previous shares or current?
I could jump to my own conclusions but would love to have some light shed by those who know more. Is it that the payouts for the previously mined block were confirmed by another pool, but those for 501835 are not (yet)? If so, why were the previous payouts so (relatively) quick after the block was mined, compared to 501835?
I'm much more curious than I am doubtful or suspicious - I'm sure the payout(s) will come I'd just love to know more about the tempo.