While creating a level, I added a curved stair case. At some point, I don’t remember when, I was no longer able to select it, and it wasn’t showing up on the wireframe viewport.
The only way I could select it, was via the scene outliner. Rebuilding geometry and/or restarting the editor wouldn’t solve it. Also, I tried both “Place” and “Geometry editing” modes.
I am attaching the level for you to verify (removed everything else in the level, left only the offending brush).