Its seems to be as solid as the other slides. There is a little flex but seems normal. You can see the bow under the slide as well. Could there be a support broke somewhere? How are the floors made?
mine is a 1" piece of wafer board tapered on the interior side with a waterproof coating on the underside.. My thoughts would be either water damaged board or cracked board. I would definately pull carpet up around the lowest point of the dip to check for cracks or water damage.. Good luck