I just experienced this on Round 2. Had to wait until carousal to get a champion to fix it. You don't need to sell a unit but instead pass over the champion and then off the menu to force the game loop to call the menu sell function, afterward it will notice the champion no longer on the menu and call the buy menu function update. You'll have access to your buy menu.
Potential Cause?
- Missing a higher level function responsible for ensuring the menu returns to default buy during an error.
- &Pointer is not being updated or missing when used for determining whether:
A Which Menu should Display
B If a Champion is over the Menu
- Missing try/catch in the function where the cursor exits the menu with a champion.
- The update for returning the menu to buy is within the sell function/Class and is failing prior to calling the default menu again due to some fringe case.
Hot Fix could be a try/catch block wrapped around the sell_menu() with the Exception calling the default menu.