Warped plywood roof sheathing - what next?

Hi folks - newbie here.....maybe a bit of an expensive fix on my hands here - the facts: - house is in Northern Illinois, approx 15 years old - we bought it 18 months ago - extensive mold discovered in attic during home inspection....mold cause assumed to be bathroom exhaust fan with exhaust duct outlet simply lying on top of soffit vent in the attic - clearly some exhaust air was going into the attic and not properly venting to the outside....supposedly that type of set-up met code - how the code allows that is beyond me - but that's a separate subject! - mold was remediated - all sheathing/rafters now covered in a white coating and the mold has not returned (so far, so good) Fast-forward 18 months..... - roofer recently at my house giving me an estimate to replace a dozen or so blown-off shingles - suspect high-nailing to be the cause, again, a separate subject - nail gun was the worst thing ever invented when it comes to proper shingle installation - arghhhh!!!!! Roofer guy asked if he could have a look in my attic, where we found a few interesting things: - rust on roofing nails (wasn't there after mold remediation 18 months ago)