If it is similar to my Kona One, you might be in what I call slow plane mode. Because the board is rockered, I am able to get it to plane from an area of the hull that is forward of the normal planing area. While doing this, the back of the board is angled downward instead of upward. This creates a lot of drag. (Imagine a level banana in the water. The front will plane while the back has the reverse angle.)
To solve the issue, I had to walk back on the board, and get used to the fact that the nose will ride higher than I expected initially. It may involve getting the mast back quite a lot too.