Interesting thing on that freekick - Spartak put a screen of 3 players to obscure Karius' view. But they put them on the wrong side of the wall. Which means I believe Karius thought the ball was going where the screen was and positioned himself more to cover the right post than the left. Because why put a screen there if you don't plan to shoot that side?
If you go and watch Coutinho's free kick tonight, or the one against Arsenal last season, you will see what I mean with how you place the screen. You put it where you plan to shoot to obscure the keepers view until the last minute. If the keeper doesn't see the ball until it's over the wall, usually by then he is already beaten due to the pace of the ball.
So he either tries to be clever guessing where the shot will go, or just simply positioned himself wrong. Either way it was a bad error and cost us which was a shame as he did the other little things right. But that doesn't matter when we concede.