Excessively low first three modes for Normal Modes analysis using spring connectors

[Anthony.StahlFNEM6]

Hi all,

I'm currently attempting to run a Normal Modes analysis on an assembly.

The model shows a plate bolted and fully constrained from the bolt holes.

The plate, along with rails and square washers are then surface contact bonded to one another.

A rigid body connector is then used to make a flat surface between the top of each square washer pair (see below).
I then offset a plane, created a sketch making four squares evenly displaced above each square washer pair, and created another rigid body connector from each square.

A spring connector was then connected between these rigid bodies.

A concentrated mass was then offset above the assembly using a work point.
This mass was then connected to the rigid body connectors above the springs using more rigid body connectors.

The spring parameters are as follows:

My issue is, when running the analysis, I get first modal frequency results far lower than I initially expected (see below):

My questions are:
- Are the springs connected correctly?
- Are either the bottom or top rigid body connectors that the springs attach to set up incorrectly?

- Judging by the concentrated mass used and the calculated stiffness applied to the springs, could the resulting displacement and first modal frequency actually be realistically correct?

Thanks in advance!
I'm running Nastran 2021.