In the tooltip you can observe zIndexes of the points. However, when playing around with the angles, it may happen that blue scatter point will be plotted behind the red one.
Yes, but it seems logical to me, the z coordinate is higher and therefore the blue point is behind the red one.
Changing z-coordinate doesn't change how is this displayed. Attached screenshots:
Fixed #3949, added zIndex calculation for scatter in 3D chart.