Hi,
Missing surfaces (or in the case of subD better names limit surface patches) might have a number of reasons.
1. They may be set invisible. There are multiple ways to set geometry invisible in the main menu 'ObjectDisplay'. Try
2. Object visibility will follow the layer visibility -- so if some of the surfaces are on a layer that is set invisible that might explain that
3. The invisible surface may not be shaded. Depending on how you are shading it will be applied only to the selected surfaces or may not affect newly created surfaces. Try disabling and re-enabling your shade mode. Do a pick nothing first to make sure the hole scene is affected. Also try main menu 'WindowDisplay'->'Hardware Shade'.
4. You might have set a transparent material for the invisible surfaces.
5. There may be more that I am currently forgetting.
I see in your screenshot that you do have 'show'->'model' set off. I advise setting it on. [You find it in the right mouse button marking menu -- if you haven't changed it. Otherwise in the top right corner of you viewport you find the 'show' menu. You can enable it there.] The wire frame will tell you if it's something like transparency or missing shade flag. (Surfaces set invisible will not show up here though).
Another thing you may want to check out is if your surfaces are still int he object lister. Picking an element in the object lister will highlight its counterpart in the scene (Unless its invisible). The object lister will also tell you if the surface or its layer are set invisible.
All this is general and has nothing to do to with subdivs. If nothing of the above helps I would be keen to know what happend. In that case some more questions:
1. Do you remember what you did before the surfaces vanished?
2. Can you share the wire file?
Hoping that this helps
Matthias
