I hope you don't mind if I say that this model is a complete mess (seriously, I don't mean any personal).
Actually not only some (but many) of the rear and some of the front windows are also see-through (only from that angle it's not apparent). For some reason, all your window components contain another window component. Exploding the outside ones make all the inside ones see through. I wonder which component has gluing/cutting features and which is cutting what... π² (although you have all the window openings cut into the walls anyway).
So my guess is that there's something with the "cut opening" feature but seriously speaking there are sooo many components nested into each other that I can't really investigate which is which and which is causing the problem.
For this particular project, I'd suggest a "workaround". There are two styles in your file now that I created. One is in monochrome mode with transparency turned off and one is the shaded with texture mode with transparency turned on. Use the styles dialogue to change the rendering modes instead of the buttons in the toolbar.
Also purged the model a bit... Hope didn't delete some components you were going to use later π
7 Nightingale Rd Extension 30 var.skp