Both Players Lose
The Japanese rules state:
Article 13. Both players lose
1. After the game stops according to Article 9, if the players find an effective move, which would affect the result of the game, and therefore cannot agree to end the game, both players lose.
Note that article 9 (about resuming the game) also applies:
Article 9. End of the game
…
3. If a player requests resumption of a stopped game, his opponent must oblige and has the right to play first.
In the official commentary, they give two examples to explain:
Suppose both players have passed, while leaving one of the above situations on the board.
In both of these situations, the life and death status of the surrounded group is unsettled (white playing at A in the second case can create a seki that nullifies black territory). Both players would like to play another move at A to maximize their score. However, asking to resume the game would let their opponent play first. Hence, if the outcome of the game swings on which player gets to play, neither player would want to resume to settle the position.
In such a case, the Japanese rules punish both players with a loss, for making the blunder of passing and leaving a decisive position unsettled.
Logically speaking, the unsettled position left unresolved could be much simpler (provided that its worth enough points to swing the outcome):
