I have no problem if they need to maintain the wallet, but at least they should mark it as unavailable.

I did, only auto reply:

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We’re very sorry to inform you that we are currently experiencing a momentary problem with the wallet and had to disable it for maintenance.

As soon as the wallet is re enabled your deposit will credit.

Thank you for your patience and we’re sorry for the inconvenience, don’t hesitate to reply to this message if you have any question.

Sincerely,
Poloniex Support Team
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they normally have a human reply to my ticket after a few days.

Hi, this morning I deposit SC (SiaCoin) into Poloniex, the block explorer said confirmed but I didn't see them in Poloniex, not even in history, anyone has the same issue?

I have a specific coin I want to invest which only lists on bittrex, please let me know if you have an extra bittrex you can transfer to me, message me if you are interested and about the fee