You can see my post and experience on the subject here:
https://www.keystoneforums.com/forum...ad.php?t=44468
Without investigation, it is difficult to tell what the soft floor could be caused by; supply lines or drains for the toilet, tub, sink, black tank flush, exterior leak, etc. In my case it was the toilet floor flange, and the saga is ongoing since I have not fixed the floor yet.
The reason it is a big issue is that we have a floor “sandwich” covered by a water/vapor barrier on top and bottom. Darco plastic under protection, a layer of wood “product” glued to the aluminum floor framing, a void space filled with rigid styrofoam, another layer of wood “product” and then topped with vinyl floor. If water gets in between the layers it will not readily dry and water wicks into the wood “product” and spreads outwards causing soft floor and after a period of time without proper drying, complete disintegration of the structural integrity of the floor.