I've seen a lot of things like that, it may people who deposit to buy coins are too many, or people who sell coins to withdraw are too many, no matter which one happens, there will be liquidity issues.
especially when the volatile are huge, just like now. the greater the volume, the greater the crisis. and once the crisis come, the exchange also have no way to deal with, they can usually do is only wait to the price volatility gone.
could i know what happened on you?