Importing blender file into unity and adding as UMA recipe seriously deforms model

Question

New to blender and Unity. I've skinned and rigged a jacket onto a base UMA male model with simple animations that seems to work in blender 2.93.4.

After I saved as a regular blender file and imported it into Unity I created a slot from the mesh in the blender file using UMA_Diffuse_Normal_Metallic material, checked overlay, create receipe, binary, calculate tangents and add to global library. I added the materials to the overlay file created. Added human male and human male DCS to race in the recipe file as well as dragged the overlay into it, specified chest, and hides male torso, I also dragged the recipe into the global library. After I added the recipe to the default wardrobe in the Avatar object, the new mesh is shown, however it is all twisted and weird. Anybody know why and how to fix this?

Answer 1

The mesh of the jacket has duplicated vertices and unconnected vertices, especially on the model's right side.

Back view (after the removal of the duplicated verts the unconnected verts had been still there)

Front view (with Face Orientation overlay)

Merge these vertices in Edit mode by selecting all vertices and then M > Merge By Distance. In the Adjust Last Operation popup (bottom left at the screen) increases the distance to 0.004. (The default value only removes 24 verts but keeps the unconnected verts on the right side.)