I don't see the 3D models when I edit the sketch via Edit Cross-Section?

Remember to keep an eye on the settings on the left when editing lines in the sketch. If the party you are editing "suddenly disappears" as soon as the sketch grid appears, you can switch between the Hide All, Display All or Hide Edited Part etc options shown on the left of the Property Browser.

If you follow our basic training material at IronCAD Academy, this is something to be aware of as we change the setting depending on what needs to be seen and not seen in the 3D scene.