Very sorry you have run into such troubles. I don't know what would be a likely cause. I really hope things smooth out. I think it was a good idea to remove the wood chips, though. Since those are from fresh wood, they would be prone to mold more than dried wood shavings. We put a bunch of huge piles of "power-company-generated" woodchips in our pasture & had problems with our horses eating them & developing chronic cough. Didn't expect that. Had to spread the piles, plus put in slow hay feeders to give the horses something else to nibble on for more of the day. On further thought, I believe fumes from some types of freshly cut wood aren't very good for chickens so maybe that or mold could have contributed to chick problems??