It is interesting the number of claims that are inspected due to expansion and contraction. Wood, laminate and bamboo all have coefficients of change. That is the numerical value placed on the amount a product expands and contracts due to moisture gain and loss. The coefficient of change is constant but the amount of visible change is greater in wider boards. So if an installed board contracts 1% the gaps will be larger in a 5" board than a 3" board.
The reasons the boards gap can be installation, manufacturing or site related. The true cause for your cupping, gaps or buckling can only be determined with a site inspection by a certified hardwood floor inspector.