It's "Error by design" which got abused by miners to mine by far more BCH blocks than they should (started parallel to the heavy pump of BCH via KRW/BCH pairing), now after some days the diff adjustment kicked in and the miners leave again as it's no longer profitable to mine BCH. As per current hash rate in 2 weeks and 2 days the diff will go down again and most likely the miners will come back to abuse that "feature" to make a lot of money in short time

Just look e.g. at POW / Regarget, POW / Hashrate, Blocks / Blocks/hr, Reward / Opportunity costs, ... at http://fork.lol