I am not sure why it had frozen. I did not have this situation before. Maybe I miss something.
To destroy the same color, or destroy a line, You might try to pick all chess, then check the color or the logic position. The logic position of each chess could be got by expression:UID2LX, expression:UID2LY of rex_board object.
logical position (x, y) = ( Board.UID2LX(chess.UID) , Board.UID2LY(chess.UID) )
Or, using Condition:Pick chess at LX , Condition:Pick chess at LY of rex_board object. The document of rex_board is at here