I think this exchange being hacked may have something to do with it:-
https://ethereumworldnews.com/cryptos-dump-as-korean-exchange-coinrail-gets-hacked/


A few hours ago crypto markets plunged losing over 14 billion dollars in just a few hours. At the same time news emerged that South Korean crypto exchange Coinrail had suffered an incursion resulting in the theft of various altcoins.