The capture on c6 seems premature, as white can't win back material directly, and is left positionally worse. 25. Be4 is a better choice to hold the position here, adding a second attacker to the c6 square, and adding complications for black's a8 rook.
25... Qa5xc5 26. Rb1c1 Qc5b6
An out-and-out miscalculation, after 27. Be4 white would be better. The more accurate square for the queen was g5, holding a slight advantage in the position.
Moving the knight here allows black to double the b-file, causing all sorts of unpleasant issues for white.