I think the weaknesses of MATS are harder to spot than for example Kepa and you have to watch more games of him to see it. He has got a good reputation as a top keeper, it seems that
mostly barcafans see this case a little bit different. He doesn't do obvious blunders very often, it's his passivity that let's goals in. He doesn't rush out anymore to get to a long ball, so he can't be late for the ball and be overlapped. When there are crosses that could be cleared he often also sticks to the goalline.
Then often the defenders get the whole blame, but if you watch every game you can see imo that the does so litte anticipating nowadays. In his first years he also tried to make the game fast much more, when he's got the ball now, he holds
onto it, and waits 10 seconds until it's safe again because the other team is back in deep position. This is especially painful to watch when you play against the bus, which was the case in most of the last matches.