I believe that's Polo's default maintenance message. The same message appeared when BTC and other coins were down for maintenance last week.
The sad part is, they literally only need to restart their node. It's possible that they are just extremely slow at doing anything, which has been the case with Polo for quite some time.
slow is not enough as a word to describe poloniex speed on several issues/procedures. the words super slow replay or bradypus, the Three-toed sloth suit the case much better.