Home Plate Edit, Possible Navmesh Issue

[MadTod]

I'm making a mod that edits Home Plate because I don't like the ruined floor or the horrible looking upstairs, however I've run into a problem.

 

For some reason when I tested the mod in-game anything I try to place (in Workshop mode) on the ground just goes through it (red outline) and isn't able to place (green outline).

 

Now as this happens to the whole of Home Plate and not just the wooden floors I've replaced I figured it was a NavMesh issue but I don't know how to fix it.

 

Any help would be greatly appreciated, thanks.