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I'm trying to create a shirt for a model by extruding some faces out a bit, but no matter how hard I try, the faces won't extrude properly. I've scoured the internet already, but haven't had any luck finding a solution. I'll add the download for the file if you want to see for yourself.
As you can see, the normals on my mesh are correct. There aren't any duplicate verts or faces.
But when applying any extrusion or solidify, the generated faces only scale out in the y axis.
Here's the link to download.