Impedance mismatch in LISN for EMI/EMC test
The grid has a zero impedance compared to the DUT.

The goal of the LISN is to raise the impedance of the grid and measure the DUT as a current source into a load resistor (1k) without having to use a current probe using reference resistors for the spectrum of interest above 150kHz for FCC type tests.

I modelled your LISN here.