It was under the rear seat, towards the middle, which I found after removing the bottom cushion trying to troubleshoot the back seat rustling sound. It wasn't attached to anything. The center strip is an elastic band.
I recently got the 7 seater, and it also had that same loose strap, which I found when getting into the 3rd row. In looking at that second row, I was thinking it could be related to the seat belt, but everything seems to work fine without it. I left it on the ground for now. I am scheduled to go to a service center next week and will ask them what it's for.
I'm not sure that's it. The ends are plastic and the elastic is heat welded to them so they won't retain anything in a crash. I think the two ends clip to each other, so maybe just a sort of bungee cord type of thing. There is something in the parts catalog in that area that I don't see on mine, but there are no parts numbers or descriptions and the diagram is nondescript. I was wondering if it was the cause for the rear seat rustling sound.