Yes, I've seen that. In my case, it's often after a surface-offset sort of operation, such as Shell or Thicken, as you mentioned you have. What tends to happen is the offset surface (the thickened part) does something strange during the feature. The feature doesn't fail, but the offset surface created by the Thicken or Shell has some problems. To test this, try your feature at a different thickness (thinner or thicker). I think you'll eventually find a thickness that "cures" the problem and is no longer see-through.
You may want to find the problem area and see if there's something you can do to solve the problem (often a minimum radius is exceeded, causing a wrinkle/fold or other problem in the offset surface). I often find some means of altering surrounding geometry or isolating the surface in this area to perform the regular Thicken or Shell feature and then manually patch the bad area of the surface to regain the thickness--without hosed surface--that I need.
Well, I found the problem.
There was a fillet between two of the surfaces. When I deleted it, everything became visible again.
I just reapplied the fillet to the edge after thickening.