Bittrex is on the wrong (short) fork. Their wallet is disabled for few days already, so I assume you did this withdrawal about a week ago. I also have coins on Bittrex, but didn't withdraw them, as I tried with small amount first, and saw them going nowhere. We can only hope Bittrex will re-sync to the correct (long) chain and resend the transactions. You could open a ticket with them. I have one opened ticket, they were answering initially, but after I offered them my help with re-syncing to the correct chain, I got nothing in reply. Hope they don't just discard our coins after they delist the wallet. Bug them, so they don't do it