When a material is created and saved using the fresnel node, the fresnel effect does not show in the Content Browser thumbnail.
Also, when editing the material, zooming in and out with the mouse wheel will cause the effect to look odd. Rotating the material with Left click and drag will cause the effect to "snap back" to normal.
*See attached images.
Reported by licensee in 4.8, but I was able to reproduce in 4.9 and main as well.
Material Viewport
1. Create material using Fresnel node
2. Use mouse wheel to zoom in/out of viewport, notice material looks odd
3. Left click and drag to rotate material viewport, note material looks correct again
Content browser
1. Save fresnel material created above
2. Note that fresnel effect does not appear in material thumbnail
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-19574 in the post.