Matrix buildings Material

Hi, so i working on a idea since few days, using the buildings from The Matrix release, and i find it difficult the randomize the windows material, they either lit all or none of them
in the blueprint it feels like they are one mesh, but when you open the level they are separated

I tried to select the windows manually in the level, i changed the material for some windows, saved, went back to my level, it didn’t work

Am i missing something to add in the scene or anything ?’

Thanks for the help