Not sure how to phrase this, but SolidWorks is literally ignoring a 3D sketch I made when it comes to making lofted surfaces, etc.
So the 3D sketch consists of a single spline on a cylindrical surface (BTW, adjusting the handles is a nightmare--when you move one, the others don't want to stay still--I don't know if this is due to the mathematics of a curve on a surface, perhaps related to the curve's degree, or a bug in SW).
When I try to click on it in the loft feature (with SelectionManager or not) I cannot select it. Graphics settings are set to high, and I can click on every other edge, visible sketch, etc. (Graphics card is AMD HD7850 2GB. I know, not ideal for SW in theory, but I have no problems selecting anything else). Outside of the feature, right clicking and choosing Select Other doesn't let me pick the sketch.
I eventually discovered a workaround--create an extruded surface from the 3d Sketch, which gives me the edge. I can select that.