Hi there, unfortunately I don’t. Have you tried to export “selected”? Just wondering, have you tried to export the garment as geometry cache instead? Or breaking it down into parts to be assembled in UE? So each part has a single material assigned?
If you are exporting as Alembic, there must be an option to assign material slots either per material id or uv tile.
I’ll see if I can find anything helpful and share here.