HitBTC are apparently not the only ones who are “failing” the Proof of Keys event today. The event is intended to prove the Bitoin solvency of each exchange. Every user is encouraged to withdraw all Bitcoin to private keys that they control. However, according to Trace Mayer and the Proof of Keys’ event’s official page, in addition to HitBTC, several exchanges had issues leading up to or on the day of the event (today).
Not all of the exchanges listed in the “failures” section of the official Proof of Keys site are currently having withdrawal issues. Coinbase pointed out that the issue reported back at the end of December was fixed not long after it was initially reported.