You're not the only person that is giving the "lag" reason,many complaining on the chats as well.
Yes,
https://www.cryptocoinsnews.com/jilted-trader-organizing-class-action-suit-poloniexBut, by considering the reputations maintained by poloniex so far, I am sure this incident might be something beyond their control. This is honestly an unfortunate situation for all of as well for poloniex.
Pretty sad considering the daily profit they make from fees.
But there were history like market giants were got hacked for millions dollar worth of bitcoins as security breaches are highly unpredictable as hacker are always ahead in the race of inventing and utilizing the new technologies.