A pot being hollowed out of a board is just not normal structure for the wood. Environmental changes (extreme heat, the heat vaporizing any moisture left in the wood....) is going to cause you issues.
If your wood has any moisture in it (you can't trust a company to guarantee a moisture content of a specific board) some folks like to turn pots and then let them 'rest' a day prior to applying finish, so you can chuck it back up to cut things flat again if need be.