With the help of this forum post:
I recreated their blueprint so I can input a list of my static meshes that are mapped to their respective hierarchical instanced static mesh components. Then it selects one mesh at random (based on rngSeed) for count times to generate a set of meshes in the game scene. However, in execution, it seems to just pick one static mesh and just duplicate that x times.
I read so many forum posts and have been stuck on this for days, so any help or nudge in the right direction would be greatly appreciated. Thank you for your time!