six Panel door and humidity

[BoatHouse]

Looking for advice -
A few of my indoor six panel doors have been getting sticky with all of the humidity this year. They are 15 years old and never had this problem.

We do not have air condition and keep the windows open to cool the house.

I have tried to "clamp" them to see if that would work, but the the problem continues.

One door eventually split in half. See picture.

Any tips on how to fix?

Thank you!