I really appreciate you looking into this - below are screenshots I took. Meshes are Nanite-enabled (aside from modular meshes that include windows).
I labeled the images where Nanite was on vs off.
The light trickling in and affecting the ground disappears with Nanite disabled, and the dots are reduced by a decent amount, but the problem still remains.
Thus far, my “best” solution has been to merge meshes and then jacket them, although I don’t know if this causes inefficiencies.