What is missing?

I took my Pacifica in for an issue and the dealership ended up having it for 3 months. That’s a story for another post. I recently went to do a deep cleaning of the interior and found something interesting. When I had both rear seats out of the floor, I saw that something appeared to be missing in the middle section under the floor. The carpet seems to be indented as if something was there but I have no idea what it could be. So here I am. Pics attached.