Besides the terrible design. Look on they logo in the main page on PC, the text "bittrex" without font smoothing. They still have not fixed typo SETTTINGS. Problems with scrolling and many other things.
Mobile version is adapted for PC, that's the problem. It's like a console game adapted for PC, you know what I mean.
I can't believe anyone would do serious trading on a phone so a mobile optimised site seems completely nuts to me. Then again I guess they'll know their demographic better than me. Sounds like a silly one.