Bent willow chairs

I have a big problem. I built four bent willow chairs. My shop is climate controlled with a dehumidifier. My shop is around 40% humidity. I keep the finished chairs inside and now the larger frame sticks on all the chairs are splitting more than usual. I’m guessing that the wood is drying out too fast. Does anyone have an idea why they are splitting so bad? Am I right about the low humidity causing too fast drying? I want to keep my shop dry so do I put the finished chairs outside to dry slower? ANY IDEAS???? Steve…....