Note the bio-growth development on the underside of the decking.
|Oriented Strand Board (OSB) decking, if exposed to crawlspace by tears in the bottom board can begin to rot, soften, and/or swell. OSB is not like plywood as OSB never recovers from swelling, as plywood will recover somewhat to near normal thickness. This is usually noted as humps, ridges at decking seams, sometimes deflecting between the floor joists.|
The six foot level will rock across the floor hump, which was as much as 1/2" height, never to recover to original level condition.