It happened to the most ICOs which their ico price will drop after listing. It happens when the investor just wants to get short profit and don't care about the project itself and also there too many dumpers especially from bounty hunters who get the bounty rewards or the airdropers who get their airdrops.
Don't blame the bounty hunter, they can't make the price of ICO fall 5-10 times. The main reason comes from public investors and private sale and maybe the dev team of that project dumping their token