New 3DS XL 3D not working properly

I have recently bought a New 3DS LL from Japan, modded it and changed the Top screen, as the old one had a problem with the ribbon cable. The Problem however is, that the 3D effect doesn't work properly. The screen appers to flicker then the viewing angle is changed horizontally and works, at certain angles, while other angles it doesn't.. I have checked mutiple times, that everything is seated correctly. The camera Tracking also works as intended, but it seems like the top screen doesn't react to the camera tracking, as there is no difference when I cover the camera or not. If someone has any idea, what could be the cause, I would be grateful.