[JRTJH]

It's probably the back of the convenience center which contains your dump valves, outdoor shower, electrical connection and city water hookup.

It seems that Keystone, in 2019 models is going more and more away from "clear open passthrough storage" and incorporating things that take up some or all of that space. For example, in the 2019 Cougar Half Ton fifth wheels, some models don't even have a passthrough to the other side, the storage goes from the roadside door to the front compartment. The roadside is completely blocked and does not connect with the storage at all.

added: These are pictures of the new Cougar Half ton fifth wheels. As you can see, there is no longer a conventional pass through storage. The roadside area is now blocked up with the convenience center and the inside wall "curves to the front". From what I can see, it appears that almost half the storage is 'consumed by trailer convenience".... Hmmmmmm