Question

does the shadow really vanish in the zero shadow conditions?​

Answer 1

The shadow vanishes twice a year for a minute. People who live near the equator pass through the plane of the solar system once in every six months.

When the vertical object is placed in the sun around noontime, the shadow will get shorter and disappeared. It reappears in about a minute’s time. It can also be said that the shadow appears exactly under the object. Hence the shadow will not vanish.