Eth transfer to bittrex should be bigger than 0.1 eth. If your amount of eth lower than this or the same your coin will be pending in the network , you'd better transfer more than 0.1 eth once more then the balance will show up. I did the experience before. if the case not like that , contact the support.
I thought it said on bittrex that it needed to be >.1ETH to show. I could be wrong. The frustrating part was finding the transaction # on GDAX. They showed a transfer ID # but I think that was an internal thing, not something to trace. I finally found the transaction # on coinbase on my phone. Was just surprised the ETH took so long to show up. And when you're new, you panic LOL!
As an aside, I'm no genius with this stuff, but I'd bet I'm more capable than 85% of the population. This whole thing is going to have to become a LOT more user friendly if anyone expects mass adoption. I guess the united states CME will help out a lot with this.