Conceding during Gardevoir ex "psychic embrace" animation freezes the other player game.
Psychic embrace follow the next sequence:
Show energies available -> drag an energy to the appropriate pokemon -> energy is attach -> damage is apply -> repeat.
If the opponent concedes during either of the last two steps (after dragging the energy but before the other energies show again) the game becomes unresponsive for the Gardevoir player.
Conceding during the others two steps doesn't cause any problem.
For anyone reading this that wants to play Gardevoir ex, if you are about to win and the game randomly becomes unresponsive while you are using the ability. Do not press the concede button, instead, close the client and open it again, the game will count that game as a win. If you press concede before closing the client, the game will count that game as a loss.
Also, since I'm already talking about this ability, does it really need to last 4-5 seconds for each individual energy? I think I'm speaking for most of the players when i say it takes way too much time to fully resolve psychic embrace.