SkyTopBuilders

One of the components that compounds the problem here is the OSB sheathing [AKA - mold candy]. As noted above, too many vapor barriers adds considerably to the issue, but the more I use OSB, the less I like it. Consider a practical example: I used to lean sheets of 1/2 CDX fir against the side of my shed and leave it there for 10 months - exposed to the weather. When I needed it, I threw it on the truck and used it. When I did the same with OSB, it fell apart in my hands when I handled it - now 7/8 of an inch thick.
Here's another issue I've seen: House gets framed, dryed in, and hardwood floor installed over 15lb felt [asphalt permeated]. Then the house sits for 3 years in foreclosure - still dryed in but not conditioned [heat/cool]. When we started work on it, patching the floor in some spots, the OSB subfloor was saturated. There was a vapor barrier on the crawlspace floor below but I could smell the mold in the OSB. Chemicals, heaters, dehumifiers, etc and we dyed it out but I never smelled mold on CDX fir on the hundreds of renovations I've done over the past 25 years
If plywood manufacturers could put a mold inhibitor in the OSB [and strengthen the glue], that would help when vapor barriers are misapplied