If the texture is passed through some node like Corona Mix, it may cause issues in the viewport. This is known and should be fixable. At this point, unfortunately, we cannot offer any solution or workaround (it should only affect viewport though - not the material editor preview or rendering).
If you enable RWS - the material might look wrong in the material preview in the material editor. This is because the preview sphere is not using the RWS mode.
If you disable RWS - the materiel might look correct in the material preview in the material editor, but will most likely look wrong in the viewport and in the rendering.
I would suggest not using the material editor preview or viewport for previewing the detailed appearance of the material, and using interactive rendering for this instead.