The band had been doing chats/jams during that extended bridge for something like 10 years by then. However, they had not played Metropolis in any form in 6 days, closing the previous two shows with LtL, and had not played Metropolis from the top in 2˝ months. James was really audibly ill that night. Like, that was one of his worst nights between 2000 and 2016. They were concerned about recovering by Score (3 days later), and that night was not exactly an easy set. Score adds another layer of confusion: this was basically rehearsal for the encore of Score, which was to be played more or less as it was on the album, creating potential for misunderstanding. In addition, Hudson Music had been filming that whole show, which probably made some things just a little bit off. So, I think that, between being anxious to end the show, and being a bit distracted by illness and everything that was going on that night, James had a brain fart.
It sounded like a worse mistake because JP and MP had successfully transitioned into the next part, which was supposed to begin with mostly JM, with some twinkling by Jordan and some jibba-jabba. This made it sound like JP and MP completely lost where they were and dropped out for a second, when in reality they had done everything right.
Interestingly, if neither JP nor MP had JLB in their IEMs, they would have gone longer before realizing his mistake. Who knows what that would've sounded/looked like.
Something similar happened in 2012. I have to wonder if JP would've kept going if he wasn't paying close attention, and how he knew to bring it back to the top of the verse.