It must have reached its search depth.
Say it looks 10 moves ahead and there is an unstoppable mate in 11. It may know you are well ahead but play a move and it now see your opponent can't stop mate.
That's a very basic explanation and I'm not fully sure how it works but I bet that's why.
It was something like this: the black bishop had a choice to take either the white pawn that was one square short of promoting or the white rook. If it takes the rook, pawn promotes on the next move and it's a queen vs. bishop ending. If it takes the pawn (which actually happened), the white rook then takes the white bishop and it's a rook vs. king and 2 pawns ending. For some reason before the bishop made its choice it was a +6, and after that it jumped to an 82.
Hi everybody, my first post here. I ran a game that I finished today through the site computer analysis feature, and I noticed something I don't quite understand: the game score jumped from +6 to + 82 after a move by black that was not considered a mistake or a blunder. In fact the position was obviously lost before that move, but the computer just realized it then?
What am I missing here?
Cheers.