Sorry to say but this game was again the typical Stegen-pattern.
He makes fantastic and vital saves, then he is clumsy or undecided in easier situations.
Whenever ANY opponent gets a corner kick against Barca, my throat becomes dry because MATS is simply below average in any corner situation.
Very rarely comes out, when comes he often misses, so most often stays on the line where he is already beaten if others make mistakes...
I think he's best when the action is fast and he has to rely purely on his instincts, in those circumstances he's a beast... But when there's a little time to think is when he looks undecided as you say... That's not say he's dumb or anything, just that the split second he takes to analyse the situation ends up betraying him, he should make his decision faster and to his credit he's done so when it comes to passing the ball with his feet...
On the other hand, defending corners has always been our weak spot and this has nothing to do with ter Stegen, obviously I wish he could help in that regard, but it's not something I would pinpoint on him or that I think is that important (when it comes to evaluating ter Stegen)... It was totally Alba's fault today in that corner, and while the GK could have come off his line, that's just a series of could-haves that involve the whole team... Don't get me wrong, my throat also becomes dry in every corner against us, but ter Stegen is not one of the top reasons why...
By the way, did he actually deflect the ball in the corner that led to the goal? It looked to me that he didn't touch it and the ref wrongly called a corner...