Almost 10 years ago, we had a roofed/screened porch and an open (non-roofed) deck built onto the back of our house. The porch and deck flooring is a composite plank.

Two years ago, during the hottest days of the summer, the planks in a couple places on the deck started pushing upward creating very definite "hills" (2'x 2' in dimension).

What is causing this and can this be fixed short of replacing the composite completely?