Thank you for reporting the bug. It's been now fixed.
> making it impossible to play anything useful. I feel like it's rendering the game unplayable.
I respectfully disagree. Let's say the previous word is FROG, and O is now blacklisted. You still can play, say, GIG, or ERR, or FUR, and earn a point. Even if you enter IF and earn 0 points, you leave your opponent with very few options and potentially force them to create an opportunity for your next move. Playing very short words has its advantages.
Blacklisting is an important feature in this game. It helps avoid repetitive and predictable scenarios. Without it, ATTRACT would be always followed by CATARACT, ENDLESS by SENSELESS, etc. You would just learn and memorize the best next step in every scenario. Blacklisting random letters prevents that from happening and actually makes the game playable.
In any case, both players are in the same situation. On average, your chances of winning or losing are not affected by blacklisting.