I have run into this problem once before in V17. It only happens when I use the new wall priority settings to bring the edge of the wall down below the top of the foundation wall. for whatever reason, the walls have these "wings" protruding. They don't show in plan, just in elevation and 3D. If I change the intersection group number in layers it corrects it, but the number changes back to a 1. apparently, only 1 and 0 can be used here. Any ideas here? I attached a screenshot to show what I am talking about. I am clueless on this one.