The shipping box is large and has empty spaces inside. Without support in the middle, the panels sag due to gravity, causing them to warp.
We had previously reported this issue regarding the large shipping box.
Try placing a heavy object on top of it again.
In this case, you can correct the warping by placing the panels upside down on a flat surface.
If this answer does not resolve your issue, please contact us again for assistance.
Doorvevor