Many thanks for your detailed analysis. We will have a look at ngspice.
The model 2N7002 NMOS … does not work because an NMOS Level1 requires four terminals drain, gate, source, and bulk. Your instance line
M5 1 2 3 Si4842DY
or maybe
M5 1 2 3 2N7002
does have only three terminals.
In addition an NMOS model will not accept most of the VDMOS model parameters. It is made for integrated MOS transistors on an IC (and some 4-terminal discretes).