Seems like the miner exploits some bug on the server side that causes the hashrate/reported shares to increase without actually contributing to the network hash. This is why it doesn't work on other pools.
I got the same feeling. This theory also correlates nicely with the bad luck the pool has.
I would like to ask the dev to confirm or deny it

A week ago I was writing about it
https://bitcointalk.org/index.php?topic=3259259.msg36659425#msg36659425and no reaction from dev.
Now MPH pool luck (un-luck

) make mining XZC unprofitable.

If I'm wrong, dev correct me.
that`s right, power of miner now is still numbers. no profit.