This is the first time something like this happened to me, I used to trust a lot in the exchanges, specially Bittrex, what happened here?
you should never trust 100% on any exchange even if it is binance which has been much better than all exchanges, you had 19 ETH, why didn't you transfer 1 ETH at a time? It is true that the fees would be higher, but at least if you had a problem you would only lose 1 ETH. and do not leave 19 ETH on an exchange like bittrex that are very famous for retaining people's funds, at least it was the case that happened in the past where many people lost money because bittrex refused to allow them to withdraw money because bittrex claimed that these people were from restricted countries, ironic that these people when they created a bittrex account didn’t have in TOS that they couldn’t use bittrex.
do not use this exchange with a dark past