I saw something similar to this happen on Cryptopia with XRY... XRY is listed solely in Cryptopia. Someone added a bunch of hashing power to XRY's mining operation in order to change the "difficulty" setting - then intentionally dropped off the mining pool. This caused the mining power to drop way down - the currently difficult block took several days for the remaining miners to solve. This effectively caused transfers to and from the exchange to be frozen. Apparently this was orchestrated by a pump group who ran the prices up on the exchange with the reduced effective supply and then dumped into the increasing price action. Be careful of these tactics!