It seems to me that already all my friends somehow encountered difficulties in withdrawing funds using polonex. Fortunately, considering this, I never sent any significant sums to it. And, as time showed, I acted correctly, because I was already waiting for the second day of crediting the funds that I sent to my account, while Poloniex reports the following:
SBD is currently under maintenance or experiencing wallet/network issues. Deposits and withdrawals will remain disabled until a solution is found, which may require an update from the SBD team. Any updates must be tested and audited before enabling.