I'm having trouble with the outfit I made

I don't actually get this problem in my game, so make sure you are checking the right package (like, not the older version of it, if there ever was). If you are, just clone a bra again and re-import the blend there. But before you do that, do this:
- your garment is parented to the rig. To unparent it, select s4studio_mesh_1 and click Alt P (in 3d view). To avoid it, make sure to always select the garment last when joining it with anything parented to the rig.
- you need inner geometry only in places where it is visible. Everywhere else it serves no purpose and only increases the polycount. It is best to delete it;
- delete as much of the body covered by clothing as possible;

And for the future, do not use automatic retopology in MD, it only makes things worse. Either model in quads and keep Particle distance high or retopologize the mesh;