Soft spot on floor

[54016Chs]

On my 2014 24 foot four winds we have a soft floor just outside the step down from the toilet level. I am sure that there was previous water damage from bathroom water source to cause it. Would anyone know if the wood under the vinyl floor covering is cheap chipboard or plywood? Hoping its plywood but that seems unlikely by the softness of the spot.
Thx

[flpat]

I was at the Thor plant where they build them, all the floors are chipboard