Weird phenomenon when passing light through a net

Just to elaborate on @Claudio Saspinski's answer, consider that for a non point source of light there are always umbra and a penumbra parts to the shadow as illustrated here (from https://www.researchgate.net/figure/Earths-penumbra-and-umbra_fig2_318124646):

For each horizontal string, there is a small umbra and a large penumbra due to the orientation of each string in relation to the light source - the light source is large in the vertical direction - and the spacing above and below the string. At each point along a vertical string, there is a larger umbra and smaller penumbra due to the horizontal narrowness of the light source and the blocking of light by the parts of the string above and below the point under consideration.