This just happened to me but instead I was sending it between Coinbase and Gdax, got an email saying the transfer was successful to the address 5a31b72f0bc41d0221e844ad and have no funds in either of my accounts. Did your funds return to your Coinbase account or the address you sent it to? It's been 3 days for me.
RE: Strange Issue when Attempting BCH Withdrawal from GDAX