Mirror Surface messed up

So I cloned the mirror from the fitness pack and I'm trying to separate it into just 1 mirror instead of 2 but I'm having issues with the mirror surface. When you zoom in in-game it flickers and disappears off and on as you move the view. I didn't change anything with the mesh and it still does this. I know that blender exports stuff with seams sometimes and you have to go back in and smooth it out...is this an issue like that? I've never made a mirror before so I'm kind of lost.