Each bittrex user has received a time sensitive e-mail today informing there customers about the removal of some coins from the exchange.
Image Source : https://www.btcurrencies.com/exchanges/bittrex-review.html
Message is time sensitive because there are only 15 days time period for the customers to withdraw there coins because after 30th March it will not be possible for the exchange to recover the coins.
Bittrex team has also issued the list of coins that are not to going to be the part of Bittrex market after 30th march. You can check the list by clicking this link List of Coins
They have also clearly mentioned that if you are unable to withdraw your coins because of any issue related to blockchain of your coin than bittrex will take no responsibility however if there is issue that can be solved by bittrex than you should immediately informed them.