I have a plot consisting of a blue surface (plotted through plot_surface) and a red sphere (plotted through scatter). The surface zorder is set to 0, and the sphere zorder is set to 1 (although not setting any zorder values gives the same results).
You can see that the red sphere is to the left of the surface:

When I turn the graph, you can see how the red sphere begins to disappear behind the blue surface , although it is in front of it :

Until the red sphere disappears completely:

It is strange that at certain angles / views the red sphere reappears and is visible again, for example, this:

? , /zorder, , / , .
, , ( , , ).