Originally posted by geo8601223. ... Nh5 looks like the culprit. I'm not convinced by your assessment that "Black was climbing all over White.", white has a pawn storm against black's king, it's risky because they're also white's king's pawn cover, but I don't think white's worse before 23. ... Nh5.
27. Qg6, Wow! Only a few moves earlier Black was climbing all over White.
Where did Black lose it? Perhaps 25...Bg3 might have saved him.