When I draw a vertical Line on top of another Line I don’t get any end point which I can snap to. An Edit point isn’t even visible when I activate PointsOn (see red ring). But drawing the line horizontally doesn’t have this problem (see green ring):
Rhino 6.32.20337.13001, 12/02/2020
How cool is that? 
Edit: And, it has the same problem even if I draw it horizontally and then rotate it vertically. No endpoint visible nor can it be snapped to.
// Rolf
And… if I extrude a horizontal Line upwards, I get the following strange visual representation (black boundary on top when selecting the extruded surface):
It looks the same in both Shaded and Wireframe mode, and the upper edge cannot be selected.
What have you done, my friends?
[Edit1]: Same problem in (6.29.20238.11501, 08/25/2020) (I reverted back to R29).
Technical render mode:
[Edit2]: Same thing with (6.25.20114.5271, 04/23/2020)
// Rolf
Hi Rolf - I need a blow by blow to repeat this; so far it all looks correct to me but I am probably not doing it right.
-Pascal
Do you have a clipping plane in the file? Or maybe the model extents is very large and you are seeing some view frustum clipping? Couple of things to check maybe…
This is really embarassing but I just discovered the cause of this: A hidden (do I dare say?) … clipping plane! (cutting off just below the top of the geometry)
Looong sigh. 
// Rolf
Ah, you saw that at the same time. Anyway…
