Moving mouse over edge + holding shift show a point (a vertex) that can be added by dragging it while shift is being held.
Sometimes the point will not appear and the edge does not get a highlight. Releasing shift often makes it highlight again.
Sometimes the edge works fine, and then, without moving the camera or modifying anything the edge doesn't highlight anymore
Moving mouse over edge + holding shift show a point (a vertex) that can be added by dragging it while shift is being held. Sometimes the point will not appear and the edge does not get a highlight. Releasing shift often makes it highlight again. Sometimes the edge works fine, and then, without moving the camera or modifying anything the edge doesn't highlight anymore