I am trying to add geometry (would like to make a cave system), but it shows up as just an empty shape (e.g. wireframe). I am making sure the brush is in additive mode. It works in other levels, but not the Earth level. There seem to be missing faces in the geometry as well, ones that move to different places when I rebuild the map. Is there any way to fix this without having to re make the whole level from scratch? I noticed if I try to add new geometry (e.g. a box) to existing geometry, the face I place the geometry on disappears as well (not the way that subtractive brush does).

Edit: It does not appear to be flipped triangles. I can look through both sides of the messed up geometry and I don’t see the “inverse polygons”. Here is the top of the “flag pole” like cell phone tower, which has been particularly messed up. It is a cylinder and a sphere, but many of the faces are missing, even when looking from behind (e.g. they aren’t inverted). When I place any geometry, the faces are now invisible, and there is only the wireframe (no faces)…

Here is a screenshot of the messed up geometry (a sphere at the end of a cylinder):