"Weld identical vertices" may not be enough. I have several clothes in which the vertices are nearly identical, but not enough for the importer. You may need a modeling app to weld them. Sometimes, marking them as "Soft Decorative" in the Cloth Room works too.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.