They must be using the IP address that has very bad luck.

I treat miners and rental sites differently.
A miner is effectively responsible for all their hardware.
So luck statistics have to show clearly that they are doing something wrong before I'll put a hold on their payouts.

A rental site doesn't really give a damn since they get paid no matter what is supplied by the source.
In fact *Hash has recently pointed out they make even more from withholders since they keep any BTC the withholder has in balance and the pool/target they were mining to will never find out from *Hash and of course never be refunded anything.
Since *Hash has a larger hash rate, withholders are able to easily hide their withholding within that larger hash rate.
Thus I'm more than willing to block an IP address that shows the early stages of bad luck - especially since no one (but me) actually loses out from me blocking an IP address, it just means an increase in variance (and less fees for me )