Note: I looked for a similar or related bug but could not find one. Sorry if it's here and buried.
Subsurface Profile materials render differently in the Material Editor Preview pane than they do anywhere else. This will make editing them in the actual editor (or the Material Instance Editor) essentially impossible, even for simple tweaks. And even if you didn't recommend editing them in that way, they just look broken within the Material Editor.
In this image, the character's skin (using Subsurface Profile) looks as expected.
Here's the mesh in the Static Mesh Editor. The lighting looks bad, but you can tell the material is working.
Here's the mesh in the Material Editor (a regular primitive looks just as bad)
To make sure it wasn't that particular material, here's the same thing with simple assets.
Sphere with a simple SSP material in a scene.
Same sphere in the Static Mesh editor with SSP material applied.
And that same sphere in the Material Editor.
In Release-4.14 branch, open the PhotoRealCharacter project (Samples/NotForLicensees).
Same done in Samples-Main branch, built to latest.
Select the head in the map and look in the details panel.
Open the head in the Static Mesh Editor and see how it renders.
Do the same thing with the M_Skin_Bust material found in Element 0 of the mesh.
For an apples-to-apples comparison, set the Preview Mesh in the Material Editor to the Bust mesh.
You can do the same thing in the Material Instance Editor, results will be the same.
Head over to the existing Questions & Answers thread and let us know what's up.