For those wondering about Dash on Poloniex :
DASH is currently under maintenance or experiencing wallet issues. Deposits and withdrawals will remain disabled as we work to find, test, and audit a solution.
Thank you for your patience in the meantime.
Poloniex is most likely updating to Dash latest software version. I doubt this is related to the stress testing as other exchanges (who have far more Dash traded volume) are working just fine.
This just concerns Dash deposits and withdrawals, Dash trading itself does not seem effected as the trading chart is not frozen :
https://cryptowat.ch/markets/poloniex/dash/btc/4hr and the trade history is also up to date.
To tungfa : maybe someone from the Dash Core-Team who has an official contactperson with Poloniex can check with them, see if they need some help or can provide us with some additional info?