Warping T&G decks

Has anyone seen a problem with tounge and groove decks warping? Deck is made with 2x6 pine with 1x6 cedar laminated to bottom - popular in churches in the 60's. According to owner (yes I know to be skeptical) boards started to warp after new OC Oakridge shingles installed in past couple of months (complete tear-off). OC says it must be that there was no 1/8" gap between boards. I say if 1/8" is good enough for 4' wide plywood, gap for 6" board need be only 1/8 of that or 1/64" Slope is only 4" and 1 layer of #15 felt underlayment.

The building was built in 1966. The ridge runs from east to west and the problem occurs on both the north and south sides. Shingles are the same dark color that have been used at the school many years. The span is 14'. I did not put it on; I was called in to figure out what went wrong.

New deck or old wood? Did you renail the entire deck like you're supposed to?