Hi, read my post to the end where I describe the solution. It basically comes down to XY-axis mis alignment. For the device to be able to cut squares, it has to move across from left to right at 90-degree angle.
My Falcon2 40W laser moved at a 92.227 degree angle cutting trapeziums. Adjusting it, I had to loosen the one side of the Y-axis movement, and let the belt jump 7 teeth until I could visually see the XY axis formed a 90 degree angle.
Also raise a support ticket, and complain about the lack of quality control at the factory. With enough complaints, they will hopefully start shipping better products.