He'd played well up until then under a lot of pressure from the Vikings constant blitz which got the better of the 49ers O line far too often. Two big moments change the game completely imo, McCaffrey fumbling in the redzone on the niners first possession, and the Vikings TD right on half time.
Steve Wilks has to get the finger out and get the defence firing again, the Vikings were only forced to punt once, and to say forced is misleading as it was their own mistakes that left them short. You are always going to struggle to win games when you allow the other team 452 yards on offense. Another defensive performance like that against the Bengals and he might not be back after bye week.