Bittrex Bitcoin wallet disabled until after BIP-91 is settled
"At this time, with BIP 91 locked in, we are confident that the Bitcoin network will successfully activate and enforce BIP 91 blocks. Bittrex will be monitoring this situation closely. We do not anticipate any issues with BIP 91 activation. However, Bittrex will close deposits and withdrawals of Bitcoin (including 2nd layer protocol XCP/OMNI and associated assets) 4 hours prior to the BIP 91 activation block 477,120 anticipated to be at July 23, 12am PST (7am UTC). "