At some point my 3D doesnt show properly, and I have no clue what happened. It is with few files already, different models, I got some kind of greyish overlay on textures in 3D, but didnt find out what it is and why there is this error.
For someone to help you will likely have to provide a more detail description of what the 3D geometry is and perhaps a few more pictures with different angles and zoom so that it is possible to understand the model.
It would also help to have information about your hardware and software setup.
Hi you most likely have to slabs that over lap and are at the same height, the solution is to either trim out one of the slabs or to raise or lower one of them by a very small amount, about .1mm, that will solve the flashing that you are having in the 3D open GL.