Question Exporting FBX from Blender makes the file incompatible with pre-export FBX?

Hello. I'm having an issue importing and exporting rigged FBX character.



I have this rigged FBX character I got from the Unity store. The white model on the left is the original FBX file and the messed up model on the right is the exact same FBX model with nothing changed but imported then exported from Blender. Now, when I try to put the original FBX's meshes into the exported FBX's Skin Mesh Renderer, the meshes no longer fit the Skin Mesh Render and get all distorted like shown.

The reason I'm trying to get this to work is because I have an armor equip system where I simply replace the Skin Mesh Renderer's mesh with the armor's FBX mesh. Armor sets from the asset store work fine when I replace the mesh in the character's Skin Mesh Renderer, but they are not compatible with the Blender exported FBXs like shown above.

Does anyone know the cause and fix for this issue? Thanks.