I started my first Underground Arena and lost my first match. I got the progress screen with the redraft button, but I clicked Back first. After that, I was unable to return to my match; instead I got the entry screen where you have to pay two tickets. I did not click it to check what would happen.
After exiting out of Hearthstone and restarting, the game worked as it should and I was able to change five cards. I was not able to reproduce the issue after the restart.
In case it matters, I did not have an active regular Arena run at the time this happened.