Monopoly Sudoku - Missing Money when I log back in

I play until I can claim the daily bonus and build on the next 2 properties (same color) on my board.  But the last 4 days after earning enough to upgrade the 2 properties I receive an error message preventing the upgrading the 2nd property.   Upon exiting the game and re-entering a substantial amount of money (15 million today)  has been removed from $ balance presenting a considerable amount of game play.