Rodrigo Gomes had given Wolves a 78th minute lead before Mohamed Salah equalised for the visitors five minutes later. But Andre then struck for Wolves on 94 minutes for the winner.
Slot lamented afterwards: "Same old story. Recently, we are picking up points because many times we’ve scored from set-pieces, but what did not change in the last five, six or seven games is that we struggle and find it very hard to score from the open-play chances that we do create.
"Not as many as I would like from all the ball possession we have, but enough and far more than the other team. But, end result, we score one and they score two – and indeed another time in extra time, so it sums up our season again in this game as well."
On conceding another late winner, Slot also said: "What I mean with ‘it sums up the season’ is that that we’ve had far more ball possession than the other team, we’ve created more open-play and in-general chances than the other team, but from open play we struggle to score.
"Recently we’ve scored a lot from set-pieces. Today again, we had a lot of set-pieces. First half, (they were) very poorly taken – a bit similar to how we played. I don’t think we played a very good first half."
Liverpool sit in fifth place, three points outside the top four.
Slot also said: "My expectations have changed throughout the season because I expected more from us than where we are fighting for now. But it’s another setback and we didn’t help ourselves with this result, not at all.
"If we don’t want to rely on a deflected shot, we need to do better, we have to play better, but we’ve had enough chances to win the game. But credit to Wolves as well, they fought from the first second until the end and got, maybe, a little bit of luck, what they deserved if you look at how much they put in throughout the whole game."