What kind of mesh are you applying it to? Specifically the one that is flashing, but since one is flashing and the other isn’t, are they both the same mesh?. Did you import that mesh, or is it just the plane actor from the starter content?
If it was imported let us know how many polys make up the mesh, and if it’s not just a single quad post an image of it in the mesh editor with wireframe enabled.
Lastly check and make sure your material and mesh are not set to 2 sided. For the material the setting is in the details panel shown above, for the mesh you can find it under the Build Settings menu in the mesh editor window