Navmesh not building properly

I've switched my project to a different version of unity because I'm on a new computer. Can't use the latest version, because apparently cloth physics don't work on that, so I'm using 2018.1.9f2 personal.
However, it appears my navmeshes are missing huge chunks of them for some reason. What's even stranger is that they always build in exactly the same way, no matter how many or how few objects I have selected. If I delete my navmesh completely and build the navmesh again, either with all my objects selected or none of them selected, it still builds the same consistent, yet incomplete portion of my map.

What is happening, and how can I fix it?

 

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The parts with missing navmesh- are they marked as navmesh static?

 

Navigation static? Yes, they're marked as navigation static.

 

Update- I just opened an old backup of my game, and now the navmesh seems to be baking on it just fine. I did add a bunch of stuff since I made this backup, though, and am trying to figure out why it's working in one version of the project and not the other. Apparently it has nothing to do with the version of Unity.

 

After a ton of trial and error, I believe I've found the problem. The very existence of one of my prefabs within my game's files was somehow preventing any navmeshes from baking properly. I have no idea how that's even possible, but I have remade that prefab from an old project version, and it looks like everything's working fine now.