Add Terrian Texture/Painting Black After a Certain Number

I'm new to Unity and I believe I've encounter a very weird bug. After an certain amount of texture added to the terrain (32+), the texture just paints black. I made sure that all texture has a martial and the terrain also has a nature martial. I spent several days trying to get this fix. I know it isn't the texture because when I apply the black texture to slot number 31 it paints normally, without any problems.

I also have a zoom glitch, when zooming out the texture isn't black anymore however when zooming back in the texture is black. When I hit play the landscape is black just like the texture.

Graphic card: AMD Radeon R9 200 Series 8 core CPU 16 Memory

Can someone please help me? I really need to finish this project soon. With this glitch I'll never finish this project.