If your point is the goal was on him, you're wrong. It wasn't only on him. You should rewatch it. There was plenty of time and opportunities to stop Verratti or draxler in that play. Unlike his mistake vs Chelsea, where there wasn't really much to do once Ramires got the ball from him.
Alba and Iniesta were both caught on their wrong feet because our team was MOVING FORWARD when Messi lost the ball in an easy play.
This is the moment Verrati took the ball from him and IMMEDIATELY passed to Draxler:
As you can see, Iniesta was at least 4 meters from Draxler. I don't know about you, but I don't expect an old guy like Iniesta to catch a younger one with this distance.
Still, Iniesta started to run after Draxler as soon as Verrati passed the ball.
What happened next?
Draxler gave the ball back to Verrati, who was completely alone, since Messi didn't track back after his own fuck up.
This moment Iniesta was completely sold (same goes for Alba since the beginning). Both of them couldn't do shit to hold Draxler or Verrati.
Who could? Busi, Umtiti or Pique, but all of them would need to leave their spots and COMMIT to TWO opponents, which is always a bad thing for a defender.
Since both were caught off guard with the wrong foot, they simply didn't have time to think about the play and to coordinate their positions and their actions, so they kept going back until it was too late.
Yes, you could argue Umtiti failed by not getting close to Draxler, but defending is always easier said than done. He would never be put in that situation if Messi didn't take an unnecessary risk, when he had passing options, as I already pointed out.