Weird Mesh Rendering Holes

I've been trying to fix this problem for about a year now shown here. I first noticed this when I was importing my meshes from Blender. I was using Edge Split before so I thought that was the problem, lately I've shifted away from it since I know how to make Normal Maps now. But when I imported my new Door Mesh, the Problem was still there. I already changed the bias and it worked but I saw a new Problem, there is a tiny slice at the mesh where you can see the other side shown here. I already double checked the mesh and it was all connected.