What it is: The center of the pieces of flooring appears to be higher than the edges.

Cause:
While it is theoretically possible that excessive moisture could cause crowning, it is more likely that the floor cupped and then was sanded flat before it could dry and flatten on its own. When the floor boards did dry to a normal condition, their edges had been removed, making them lower than the center of the board. Gaps are generally formed as the flooring dries.

Cure:
First, determine if the moisture content is normal and if all of the crowning from the original cupped condition has occured. After the floor has stabilized, resand and finish.