We have the same issue with our product aswel. From the date of purchase, the V groove tool would work correctly on panels below approximately 1 metre, anything above that it wouldn’t work correctly. At the top, it would go down roughly 30cm and work, fade out in the middle portion and resume grooving for the lower part of the board.
We have tried various different things to change the outcome, but haven’t got any luck with it. Wondering if there is something we can do to solve the issue.