this unfortunate event has been haunting exchange users not only for bitfinex.  exchange administrators are following strict compliance set by the government they are registered in and also the government the user is from.  a lot of technicalities are involved that's why sometimes it takes longer for transactions to be successful.  one particular issue that can trigger this is the anti-money-laundering act in which governments wants to monitor the movement of funds of large transactions and big-time users.