I don't know. Bittrex didn't respond to our outreach.
I'm sure it had to do with the fork that happened after a miner suddenly pulled 1.2 exahash from Uno.
Now Bittrex joins a long list of former UNO exchanges:
Safecex.com, Shapeshift.io, Btcpool.exchange, Altquick.co, Bitebi9.com, Cryptsy.com, Coinbroker.io, Coins-e.com, Allcrypt.com, MintPal.com, Atomic-trade.com, Comkort.com, Coinedup.com, Coinex.pw, CryptoRush.com -- Bittrex
hello are you DEV's UNo Team?
Please come over to the telegram group. The death and Community leaders are active over there. Here is the link.