Because timber is a 100% natural product, warpage may occur from time to time.
Some factors that may result in a warped benchtop include incorrect transport, long term storage before installation and changes in temperature and humidity.
Recommended fix: leave your benchtop on a flat surface for at least 48 hours. For natural timber and bamboo; once flattened, ensure it is sanded and sealed accordingly.
When fitting, make sure your benchtop is fixed to the cabinet.