SketchUp's tolerance is 1/1000" That's' pretty small for most use. But if you are making a small thing - say it's a tiny chamfer in woodworking, or a rounded-corner for 3dPrinting - then you'll run into issues. SketchUp can't create edges shorter than that - it simply takes their start and end points as being coincident, so it skips making them. A missing edge means a missing face that needed that edge. The work around has been discussed in many threads... I'd recommend that you make the 3d object as a component. The place a second instance to one side, and scale it x1000. Then do your small size work within an edit of that. There'll be no issues of tiny geometry. When you are done delete the x1000 version. When you look back at the original sized version the tiny geometry will be there. Tiny geometry can exist but it cannot be directly created !