Thank you for the research @glitchered !
You are right, so I have been trying to get it broken again, and I achieve some little evidences, but not clear enough to post them. I have tried with many small “floors” (1,1,1 scale) and it works mostly well. It could look like something related to scaled meshes then, but I have also tried with a nonscaled unique floor and errors will occur more frequently, so it seems more related to just big meshes.
Anyway, in my house project, all meshes are 1,1,1 scale but these “propagation issues” are huge. But yes, it seems to happen mostly on biggest wall meshes (even if not anything crazily super huge), and it punctually happen in small meshes too.