I checked the post in Poloniex saying that there's an ongoing maintenance and that will have an affect deposits and withdrawal. Any news when this maintenance will be completed and if there really is an ongoing maintenance? I see in Poloniex its not only ZEC have this message there are other alt coins too.
My experience with Polo in the past has been if you ask whats going on you will get silence untill about 2 days after everything has gone back to normal at which point you will get some generic response which, in this case, would be something like "We were doing mantenance on the wallet and it is now complete" ¯\_(ツ)_/¯
Apparently even the zCash team doesn't know what they are doing:
https://forum.z.cash/t/polo-zec-wallet-disable/18793/9I did see Bittrex claiming a possible vulnerability in the Z family that they were investigating so they took their wallets offline as a precaution but they also said their zCash wallet would probably be re-enabled soon so dunno if thats related or what, because the Polo wallet has been offline for ages.