Id doubt its because you have TOO much moisture.

I would think the vapor barrier type deal you have is doing its job, those crawl spaces aren't airtight and air will get in there and move it around and out from under the house.

Id just bet like I said, its lack of insulation.

Youve got cold under the house, and warmer possibly more humid air in the house and its condensing on the wood between the two, then your getting the mold and separation of wood.