Solid Meshes that are not solid ...!?

can anyone tell me what is going on here? see the tank turret , all my game is made out of 2d sprites, including the tank body and tires, but the turret is made of 3d polygons, and it has 4 pieces that insert into themselves so the parts can move when the tank fires, it was working good so far using unity standard shader , but I upgraded recently from 5.3.7 to unity 5.6.1 and I see this half transparency / additive FX on the tank turret, I have tried different shaders , touched here and there, but can't find one that looks good and avoid this transparency thing.

the up screen is the game window, the bottom is the scene Window, I also don't understand why in the scene I see it right and then wrong in game window...

thanks in advance

 

Are you scaling the mesh to be flat in the z plane?

 

hey! thanks for the help!

I have fixed this issue, the problem was that I am rendering to texture, I create that render texture in code and i was not setting any depth buffer cause , in previous versions of unity , by default the render texture was created with 16 bits depth, so to me the depth buffer was not something I was even aware of ... but in new unity 5.6+ versions by default is created with 0 depth , just because.... well just because no reason I would say ... at least no reason other than breaking your game lol.