The mesh outline is not visible when extruding or moving along the axes. The axes overlap the faces of the mesh themselves, and because of this, it is not convenient to precisely position the extruded faces.
It exists on all versions of the 2.8x blender.
To repeat the problem, you can select an edge in the editing mode and simply drag along the y axis. In this case, the contour will not be visible by how much it is moved from its actual position.
With the same action in 2.79, I see black the contours of the mesh as far as it changes when moving.
Bring it back as it was in 2.79