Objects are showing up transparent in substance painter, but all the normals are correct

So I'm building a model in maya. There are a bunch of repeating parts, except they are mirrored. No problem, duplicate, transform -1 on the appropriate axis, freeze transformation, delete history done!

Everything looks fine in Maya, but when I bring the models into substance painter, the buildings that I duplicated and flipped are showing up as transparent: https://imgur.com/fPXAdWS

Now I know what you're thinking, your normals are flipped. But here's the thing, I don't think they are. Here's the normals displayed: https://imgur.com/a1LMs3V

And if I flip them anyway, this is how they look afterwards: https://imgur.com/XS7u74V

And this is how they look in substance painter: https://imgur.com/jkzIwy7

I still feel like this is some kind of normals error, but I can't figure how what the issue is, or how to fix it.

Any ideas?