Do you actually care about a 24mOhm resistor?  Generally, these resistors are in series with much larger nonlinear resistance (eg, the junction of the diode), and 24mOhm is irrelevant, but removing it makes the circuit matrix smaller (and less prone to numerical problems).

Spectre is not doing anything to the netlist. The message indicates that the MOS model itself considers the resistor to be negligible and so is ignoring it. If you feel the resistor is significant, there are steps you can take to assure it is included in the simulation, but that is very unusual. In almost all cases you are safe in allowing the resistors to be neglected.

-Ken