Clipping issue

Hi. Some CAS items are made of more than one meshgroup for a reason: to tune each of them differently. Each of these meshgroups has a cut number assigned to it, which is how The Sims 4 studio understands which 3d models and in what order to import from a blend file into the package.
Your blend file has one meshgroup, meaning you must import it into an item made of one meshgroup. You are importing it into something that has more than one meshgroup and only the one of them that has cut number 0007 is being replaced with your garment.

The default size of the uv space in most if not all software is square. The Sims 4 textures, on the other hand, are rectangular. When you apply a rectangular texture to uvs that were generated in the square uv space, they stretch vertically. So before placing them, you should shrink them back to the original size with S Y 0,5.

Do not join the body with the garment until you make the later fully functional. uv_1 and weights never transfer right to the body.

Your mesh is affected by foot bones. If you import a blend into a package started from something that is not affected by them, you will get distortions. If you won't, someone else using your cc might.
To my knowledge, no base game item made of one meshgroup is affected by them. You have three options:
1). split the mesh into meshgroups the same way whatever you cloned is split and remove extra ones with this addon;
2). remove foot bones, assign rig in Armature modifier, Normalize all weights, clone a lingerie set and import the blend there ( keep in mind that this may affect how the mesh animates in the foot area);
3). clone yfBody_Bonus01SWarsAayla, export the blend, append s4studio_mesh_1 from it into your blend, remove the same amount of fingers from your garment, save, import the blend into the package, change ExcludePartFlags from 000000000FC0E100 to 0000000000000000.