The first goal of Bilbao is on him. He drops in the backline, like he did under Guardiola to help the deeper buildup, but is so slow to get back in his position that the team at times looks broken.
Not only does he go out late, but when he does, he presses like an idiot when it was clear he was gonna be 2nd on that ball and gives Raul Garcia a free path for an easy assist down the middle for Inaki. Just a fuck-up from start to finish and he does this shit several times a game. His legs are just gone (considering he was far from an explosive mover even in his peak), and in that position, they are very important.
Lenglet also is to blame because he was turned with ease by Williams as if he was some amateur CB. As far as I know, Inaki is right-footed. He was always gonna be tempted to put the ball on his right for a safer finish and a cleaner hit.